Fediverse also makes it potentially easier to scan for this stuff. You can just connect a new server to the network and if the material is on federated servers, then you can find it (probably). While if it's some private forum or even the dark web, I assume it's a lot more difficult.

The other thing is, most regular servers defederate from suspicious stuff already. Like pretty much nobody federates with that one shota instance, and they only serve drawm stuff (AFAIK). So I don't know if you can even say servers like that are a part of the Fediverse in the first place.