It’s mostly how big it is, the lax moderation policy, and all the effects of those that make smaller servers not want to deal with .world. As far as I know, there is no drama about this, .world is just big and that causes problems.

A similar thing on Mastodon is how Mastodon.social is the most commonly restricted and defederated server (meaning that you only see posts and replies coming from mastodon.social if you are following the poster/replier) simply because otherwise federation would DDOS smaller servers. The instance i am on now restricts mastodon.social, and the one i started on was fully defederated from mastodon.social. Mastodon.social has a pretty identical reputation to .world, and similarly to .world pretty much all the celebrities are there so defederation is a tough call for admins who chose it.