It seems to me like a law of nature that every managerial function seeks to increase its influence and headcount by definition. Without a constant and vigilant effort to keep this tendency in check, every managerial organization will keep growing and adding bureaucracy just to justify its own existence and increase its reach and power.

I think the root cause of this tendency is the law of the least resistance. Creating new things is hard, especially if they go against the conventional wisdom. Supervising and managing things is easy, especially if the people being supervised are professional enough not to need much supervision. Then the managers job is basically just to stay out of the way, which is quite easy.

Of course even managers get eventually bored if they feel they have no impact. That's when the reorganizations start. That's also when the best time to actually create something new ends.