When it comes to ActivityPub c2s (client-to-server), I understand why it's unpopular and not widely supported.
Mastodon and Loops have wildly different APIs, and it would make no sense to try to adapt c2s for these platforms because then you have to duplicate validation and other logic, and for what?
The 2 people who actually use this?
A unified ActivityPub API for s2s would only work if every implementation handled every schema the same way, and again, difficult to get done.
s2s for the win