I have seen other steam forums with their own (not Valve) modarators, and i think it reflects back on Larian Studeos what is allowed there.
ect. you cant even enter the ESO forums with out owning ESO on Steam.
Zenimax is a rather larger company than Larian, however, and can dedicate more staff to social media and the like. Otherwise you're talking about volunteers, which comes with its own potential issues.