That would go against the concept in a pretty big way. The entire idea of federation is that each instance owner has control over their own instance, and people should (once they get a handle on how things work) move to an instance where they like the rules and admins.
If users of an instance start brigading around the fediverse and being assholes, and the admins of that instance refuse to take action, other instances can choose to block that instance as a whole (defederation) as a last resort. A user getting dropped into an instance like that, full of assholes and isolated from the rest of the network, would be way worse than just some initial confusion.
Also, should mention that the devs have been very vocal that they want to design the system in such a way that they can't control it, but each admin & user has full autonomy rather than centralised control.