Apparently some male user(s?) from lemmy.world and sh.itjust.works went to a feminist sub/magazine/whatever on beehaw and was posting explicit pictures of their junk. I suppose the admin tools aren't there to automate preventing it, so they just defederated?
The owners/admins of any of the instances aren't mad or anything, they just disagree about how to vet users (or vet at all), so until there's better moderation tools, they just defederated.