Steam

A couple of structural and ideological problems at Valve lead to this. First, the company's "flat" organization where people work on what they want means that unless somebody wants to volunteer to mod Steam communities (which no sane person would), they won't bother. Further, even if someone wanted to mod Steam, they'd have to consider that it might be damaging to their career because "I remove racists and nazis from Steam" isn't going to get the same kind of good performance reviews that some big sexy project will (even if it never releases).

Second, the leadership are rich white libertarians. They don't care what their users say or do because of nonsense beliefs so long as they keep making money. The only thing that might get them to take action would be if this kind of thing became a big scandalous news story, because at that point it might be viewed as a threat to their bottom line, but that never happened with the child gambling so it's still unlikely.