lemmy.world has had a handful of back to back queerphobic trolls spamming hate across multiple groups and instances.
They would get banned and come right back.
The reason they were able to do that is because of the open signups on lemmy.world.
Beehaw is an instance that takes protecting their members as their highest goal. They value it significantly more than wide federation.
And so they blocked lemmy.world, as it was a source of bigotry towards their members, and there were no other moderation tools available to them to resolve the issue.