Yeah my exact experience on activitypub. when i got to point running my own instance, because I federated with a larger instance like bitcoinhackers, I immediately got blacklisted from a large portion of the network. also because i didn't publicly state a speech policy, that also blacklisted me despite it just being me and one other user on my entire instance.
They banned mostr.pub.
I use this analogy a lot. If centralized platforms like X, Instagram, WeChat etc were led by monarchs, all ActivityPub instances are owned by feodal elites. No average person run their servers to socialize, they hop an instance and obey their rules. Some smart folks realized deplatforming in there (shoutout to nostr:npub1qprptnnuwnqc6h6wxc2q07rfwcmj7cfc6g4r5dgnlkxaysmpr0mqc5365p) and start to migrate, but they are very few. These so called elites are so insecure that doen’t digest the posibility of competition.
Like a wise man said: It’s a damn shame!