The main problem with centralisation

If the majority of user and communities live on a the same instance, and that instance goes down or becomes to toxic to keep federated then fediverse loses a large chunk of its whole. While if it a tiny instances that dissapears only a few people and communities need to migrate.

General i also think its beneficial if the owners of an instance are the same people from the communities its hosts. The role of general use instances should be more like a backup mirror