Wikis like Fandom typically make it easy/easier to create and edit pages. Wiki editors are rare and you want to make it as easy for them to latch onto helping and volunteering as is possible.

Maybe a fediverse option isn't needed (though the below comment's point about having a central account would make it easier for a lot of users), but having a convenient and easy way to create a wiki for your favorite fandom, without using Fandom would go a long way toward breaking Fandom's hold over the entertainment sections of the internet.