Why is the gene regulation in eukaryotic cells needs multiple level of control than in prokaryotic cells?
I think you need to consider the overall amount of information that is needed to implement a proper control system in living organisms.

In prokaryotic cells, in most of the cases, you will find that one gene code for one enzyme, so if a simple organisms need 500 enzymes to stay alive you can expect 500 genes that code for that enzymes.
A more complex organism may need 100 times more enzymes to stay alive and so theoretically 100 times more genes. Now, evolution wise, to have a linear increase of DNA vs complexity is not a good option for very complex organisms. To keep everything compartmentalised in one single membrane is also not a good idea if you need to run millions of chemical reactions using thousands of enzymes that can cross react and need different optimal conditions to work properly, so multi-compartimentalization is a must.
Linked with it arises the problem of sending the right enzyme in the right place and this has been solved by adding tags, transporter enzymes, etc... in the pot... So, lots of more information is needed to make everything run smoothly.

It turned out that an efficient way to code for all that enzymes, tags, promoters and other regulators without increment the size of the DNA too much is by multi level control of the expression of a gene i.e. the same gene can be used to produce different enzymes (splicing etc...). The tradeoff to pay to have a more compact genome is to increase the complexity of its control system.

Lastly, consider that differently from normal electronic controllers, the biological one do affect each other. A biological controller system may produce an output molecule that interact with the system under control but also with other reactions going on all over... that is another burden that require an increase of complexity in the control system to make it work.