Pawoo.net federated with mastodon.social a while ago and the euros and leftists americans complained about all the jap language posts and anime artwork. I think mastodon.social blacklisted pawoo because of it. The mastodon.social admin/lead dev is a german lolcow obsessed with "fascists" and that server's federation blacklist is large. He uses the server's size to threaten other server admins to remove speech he doesn't like. Given most server owners just want a fun place to shitpost so growth isn't a priority, they tell the g*rman to pound sand. There used to be a ban list with reasons and links to the offending posts.
Here's one. The old list had a server ban reason "transphobia" because someone joked that a politician "didn't even fap to traps". Its a small clique that controls the majority of Mastodon and the "default" instance size is used to keep their control. Peertube is slowly becoming the same due to Framasoft's political leanings.
Also, some mastodon mobile app devs updated their apps to prevent you from signing onto Gab.
None of this should be a surprise to anyone who has watched leftist behavior on social media.