Servers defederating themselves from others with policies they don't agree with is pretty common, especially if those policies are considered problematic. But I don't know what to think about the fact I can't see Beehaw mods specifying any particular instances of issues stemmed from users of those two severs, and it seems like the only criteria for defederating was the size of those two servers.
But I guess they have the freedom to make whatever rules they want for their own sever.