If you're referring to Beehaw defederating Lemmy.world it's because beehaw has a pretty strict content policy (you even have to write a little essay about why you want to join and what value you'll bring to beehaw). Lemmy.world had open sign-ups without much in the way for preparing its users for what was expected of them on beehaw communities so there was some culture clashes and beehaw decided to temporarily defederate until Lemmy has better moderation tools in place.