Short version is that for the most part forum moderation for each game is left up to the devs or whoever they appoint, and users can create user groups and curators without much if any restrictions and they don't particularly give a shit what content the game you want to sell has. The only real exceptions are if it's illegal in the US, which applies to very little (for example no CSAM).

I find it interesting that the federal government threatening a private entity with legal repercussions if it doesn't restrict the speech of it's users isn't such an obvious violation of the first amendment that lawyers aren't climbing over each other to fight this one.

And if you don't see the problem with it, imagine we agree that the federal government should be allowed to restrict what expression can go on on internet platforms content-wise, then imagine Trump and his cronies deciding where the borders lie. They already want to revive the Comstock Act.