There are also instances made to host spam bots (when they host it themselves they can make as many bots as they want and as fast as they want without having to worry about captcha) and instead of blocking each bot manually, our admins have the option to block that bot instance entirely. That's a pretty powerful moderation tool. They may of course also use this to block communities with a different ideology than them to avoid conflict. If you don't want this, you can join an instance that doesn't do this (that choice is the cool thing about the fediverse) and you could even host your own instance if you have the know how.