There's a shared covenant and there's shared block lists, both of which heavily influence what the norm is on the larger Mastodon network. Perhaps an even larger dynamic are activist-type admins that have an extremely low tolerance for content countering their political beliefs and will blackmail other admins into enforcing a block of a user or entire instance.
None of this is a shocking revelation as a large portion of older Mastodon users are known for their excessive safety-ism. It's a perpetual conflict on the network versus those that want to be more forgiving and pragmatic.
Anyway, the bottom line is that mainstream Mastodon is a left to far-left network, and content is moderated as such. The idea "just pick another server" doesn't really apply.