At the beginning of the great migration, they got overwhelmed by troll harras accounts, that used lemmy.world and sh.itjust.works open registration to evade bans. A lot of vile stuff got posted (like photos of murdered drag queens). They decided to defederate from both instances temporarily until they have better mod tools. I don't think it was necessary but they do that they think is the best for their community. At that point Beehaw had some of the best communities through and many people were angry to get kicked out for something that wasn't their fault.