Good point, I just used the first hit on kagi to source the claim but you are right.
What's wrong with Fandom?
They have the SEO juice to push out and replace dedicated wikis as the top result, even when there are long-standing dedicated wikis for the game/universe. Fandom wikis then typically have maybe half of the information from the dedicated wiki PLUS a bunch of intrusive ads. There's no instance that I know of where a Fandom wiki popping up for a community was a positive unless they simply didn't have one to start with.
You also can't really get the info out if the community decides to change wikis.
Are the obstacles technical or legal? I vaguely recall most wikis on wikia being CC-BY-SA, but it's been a while.