That other reply/summary is a pretty biased hot take. Click on that user and see where he’s coming from and you might see why. I’m not on Beehaw, but I’ll take a shot at doing better.
Beehaw has the goal of being a “safe space” on the Internet: no harassment, no trolls, very supportive of marginalized groups, etc. So they’re heavily moderated, but they have (or, at least had) a small mod team.
When the Reddit exodus started, with the sudden flood of people to Lemmy overall, two of the bigger instances, .world and shit just works, had open/instant registrations without any verification. Apparently people were signing up on those two instances and harassing/trolling communities on Beehaw, and their small mod team was overwhelmed trying to keep everything within their stricter policies. They said the mod tools available to them currently don’t allow much granularity, so about the only thing they could do is defederate from the two instances, and that’s what they did.
They said they consider it temporary until the tools or situation improve to the point where they can better handle it.
I personally think their goal is noble, but I’ve never seen anyone succeed at making a completely safe space on the Internet, and I’m not sure a federated instance is the place to make one, but good on them for trying.