Parkinson’s Law is of course that work expands to fill the time available for its completion. Corollaries of this include that’s why you should always ask a busy person to do the task for you.
Parkinson also had much to say about bureaucracies, but not quite this point:
Government expands to fill the pool of the governing class who need it. Rob, in comments.
We might slightly alter that to:
Government expands to employ the pool of the governing class who need it.
There is no other explanation for much of what government does than that.