How am I supposed to update PostgreSQL on Windows, once installed, without manually installing new installers?
You don't want your system to magically upgrade the database software, because that is always downtime (typically short, but still).

You have to take the time to plan and schedule it. It's not all that complicated as you present it.

Also, as detailed in the answer to this question, there are sometimes additional tasks to do that require reading the release notes. These tasks can be automated, but you still have to plan for each minor release.