People running private servers can be all sorts of groups, however Mojang wanted everyone to behave to their rules, which didn't fit for some servers (like 2b2t). Mojang's rule enforcement has never been consistent, and people were afraid to get banned over minor nonsense.

How it ended up is that people didn't want it started using "No Chat Reports" mod alongside their mods, which blocks the way Mojang verifies message authenticity for them so no report could be considered legit.

Servers can force this verification to work to send messages, or not require it. They can also use this mod on their servers to break the authenticity mechanism for all players on that server. Most servers will have it disabled; but the biggest ones keep it to hold their public images safe to parents.

Essentially, they added functionality where you can report messages and get people banned globally from all Minecraft servers. The problem was that they had stuff on there like griefing and swearing and "harassment" (which is very loosely defined, a server I ran had someone complaining it was harassment that a player made a second joke about them in the context of the game. Six months after the first one.). Stuff like that should be managed by the server admins, not mojang. There are good reasons for such a system I think, such as child grooming, doxxing, or inter-server harassment.

Also, Minecraft servers are all privately run except for realms.