Genuine question!
If they were individual internet forums, people would just leave instead. Reddit acts as big single-sign-on that heavily biases users towards its existing subreddits. The fact that reddit admins still allow a small group of people to moderate hundreds of subreddits for decade+ is proof of that. If they cared, they would mandatorily recycle them
In any bureaucratic organization there will be two kinds of people.
First, there will be those who are devoted to the goals of the organization.
Secondly, there will be those dedicated to the organization itself.
It is the Iron Law of Bureaucracy that the second group becomes more powerful than the first- and this is why the simplest way to explain the behavior of any bureaucratic organization is to assume that it is controlled by a cabal of its enemies. Because, by that law, it is.