Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant:  Human: Why has the world not yet agreed upon using one set of units (i.e. meters for distances and kilograms for weight) everywhere?

Assistant: The most obvious reason is history. When you have used a system for as long as anyone can remember, a different system will seem strange and probably even wrong.
Also if e.g. gallon should change to Liter that would make the prices rather hard to comprehend, - at least for a while.
Also there is pride. Our system is better than your system.

But there is some movement and e.g. NASA is using the SI-system (meter for distance etc.) in most projects.

Human: But wouldn't unifying the SI be globally beneficial?

Assistant: 
Yes, unifying the SI system would be globally beneficial in several ways:

Improved accuracy and precision: The SI system is based on scientific units that are well defined and standardized, providing improved accuracy and precision in scientific and engineering measurements.

Consistency and interoperability: The use of a single system of units across different countries and industries would reduce the potential for confusion and errors caused by using different units. It would also allow for improved interoperability between different systems and industries.

Improved international cooperation: The adoption of a single system of units would promote international cooperation and collaboration, as well as facilitate communication and understanding between people from different countries and backgrounds.

However, it's important to note that the transition to a single system of units would require significant effort and resources, and may encounter resistance from those who are attached to their existing systems. Additionally, the cost of conversion and retraining may be a significant barrier for some countries and industries. Nevertheless, the benefits of a single system of units would likely outweigh the costs over time, and it would be a positive step towards greater global cooperation and understanding. Yes, unifying the SI system would likely have many benefits globally. Some of the benefits of a unified system include:

Consistency: A unified system would ensure consistent units of measure across the world, reducing the risk of misinterpretation and improving accuracy.

Simplicity: A single system would simplify measurements, making them easier to understand and use.

Interoperability: A unified system would make it easier for countries to communicate and exchange data, improving global collaboration and cooperation.

International trade: A unified system would simplify international trade, making it easier to compare prices and products across borders.

Better science: A unified system would allow for more accurate and precise scientific research, leading to more advanced technologies and innovations.

However, it's important to note that changing a long-standing system is not without challenges, and the transition would likely require significant effort and resources from countries around the world. Yes, using one system would be beneficial. There will be an initial cost to change though. But sure, in time it would be beneficial for all to use the same system.

Also remember the good olde joke 'standards are good, that's why we have so many.'

Speaking one language all over the world would also be beneficial. Yes most people do not want to, at least not if they have to give up their mother tongue. It's not exactly the same, since a lot of the culture is bound in the language. But I think it is a good way to understand why changing to one system is not so obvious, even if we can agree that it is beneficial.

TL;DR: Yes, but it might not be as easy as it sounds.