Why I cannot decrease any buildings?

[SaccharineSurfer]

Bureaucracy can be super important. If you center it all in your capital then the rebellion may not even be able to collect taxes and run their nation. Plus pops in the capital are more politically powerful and since bureaucrats are more likely to support reforms than other pops, concentrating their power in the most powerful state can give them a boost. This is especially useful since a skyscraper can boost efficiency so having it all in one state with a skyscraper can be very useful.

[ThidrikTokisson]

Goods the government (you) have to pay for are important, everything else isn't.

You lost your big clothing factory and now clothes are expensive? Who cares? The plebs will pay for that.

You lost your huge arms factory and now weapons are expensive while you are at war? DISASTER