The fediverse is deliberately designed not to do that as federation is not cheap in terms of computing resources. I believe it’s exponentially complex as the number of federated instances grows, at least that’s my understanding with Mastodon.

Yes, federation isn’t a passive thing that the instance does. Think of it as us living on an island and striking forth as explorers to make new trade routes with other lands. We can only know about those other lands if one of our explorers has sought them out.