Worse yet: Fandom has a policy of not deleting inactive wikis, even if the community has deliberately abandoned them to move elsewhere, and will treat any attempt to advertise that another wiki has been created as vandalism and will block users (even wiki admins!) who attempt to do so.
This means that, if a community does decide to move their wiki off of Fandom, they have an uphill battle to "beat" their old wiki in search results. In many cases, Google will treat the new wiki as duplicate content and suppress it in search results unless pages are substantially rewritten.
They penalise duplicate content because 999 out of 1000 times it's spam. It's a bit of an issue forking any site, and one reason you might be better off just starting over.
This means that, if a community does decide to move their wiki off of Fandom, they have an uphill battle to "beat" their old wiki in search results. In many cases, Google will treat the new wiki as duplicate content and suppress it in search results unless pages are substantially rewritten.