Apparently Reddit has now banned a subreddit dedicated to the Fediverse Reddit-alternative Kbin:
https://sakurajima.moe/@chikorita157/110517156242412322
If you're on a centralised platform like Reddit, this is what they can do. Centralised platforms have all-powerful leaders who can do whatever they want, and you have no alternatives if you disagree.
The point of the Fediverse being on lots of servers is that each server's power is limited. If you disagree with one server's actions, you can move.