I think its fundamentally more difficult to host communications services where spam is possible and there is no auth/contact system in place before first communication can happen.
I'm not an expert in this area but from what I understand what was once novel content spam filtering is not at all novel now, there are easily trainable model strategies (BERT?) that get you to 99%.
A whitelist, auth/contact is ideal for messaging without spam and is more workable with a large federated group that can adopt an evolving open source protocol.
