There's probably more than you think -- they can just hard to find due to the shortcomings/user hostility of Google, as has been discussed here recently [0].
As a concrete example, searching for "Rabi-Ribi wiki" for info regarding a somewhat obscure 2016 Japanese platformer bubbles up the usual Fandom spam garbage to the very top, followed by a copycat site "PCGamingWiki", followed by more generic information such as its Wikipedia page. It's only if you get to the second half of the second page results that you'll find a link to RabiDB [1], which is extremely comprehensive, ad-free and documents pretty much every detail about the game.
In a similar vein regarding the original comment, there are a lot of forums with very active user bases that will never show up at the top of Google results. I still post in one regularly with ~300 daily active users who have all known each other for years, for the most part. We'd never show up anywhere near the first page of a Google search result, though, so we essentially don't exist on the modern internet. I imagine countless other forums are in the same boat.
What do you mean by PCGamingWiki being a "copycat site"? Copying who? It's always the go-to site I use to check various technical details on games and any tricks that can be done to improve shortcomings of especially older games.
I don't know that they are exceptions. The wikis for moderately popular but kinda niche games are often in good shape. For example, wikis for The Long Dark and the Kingdom series are two I've used in the recent past. Detailed information. Even the comments are good.
Both games are fairly popular within their spaces, but not mainstream or AAA.
