Watching the decentralized content moderation process play out, I am struck by the social pressures between admins.
People don't want their content showing up on an unwelcome instance, and they don't want to see content from that instance.
Because we exist in a distributed network, simply blocking another interest isn't enough to prevent this issue; mods want their distributed network to follow suit, as well.
So, decisions to federate are social. Admins put pressure on each other.