but it doesn’t stop them from existing on the fediverse.

Well of course, nobody has absolute power over the fediverse like that. Anyone can start an instance and create millions of bot accounts if that’s what they wanted. But “the fediverse” is only what it looks like from the point of view of your instance. If stuff is blocked or defederated, it may as well not exist.

The point isn’t to eliminate all bad behavior on the fediverse (that’s not possible, by design of the system, and that’s good). The point is to allow users to seek towards those instances that keep bad behavior out.