My understanding for Beehaw specifically is that it was a temporary measure to guard against the huge influx of users, as well as a way to stop trolls from creating duplicate accounts from World (since it’s popular and has open registration). Defederating gives them time to figure some things out and scale up if they want to.

The moderation tools available in Lemmy currently are a bit lacking so it put too much burden on Beehaw staff to moderate users from instances that allow fully open signup. Beehaw was seeing a large influx of trolls signing up on open signup instances and causing a lot of problems over there which eventually pushed the matter. For those unaware, Beehaw prides itself on keeping a tight lid on tolls and negativity so it was really against their ethos to not be able to keep up with it.

It's worth noting that there is no hostility or anything between Beehaw and the other instance admins. Both sides admins have been openly posting about their discussions and both sides are looking forward to refederating as soon as the mod tools in Lemmy improve enough to do so.

.world doesn’t require as stringent verification and beehaw mods claimed that a lot of spam was coming from .world. I don’t know if that’s true, but that’s what they claimed.