The default is that Valve does moderation, and if you don’t opt-out of it, they consider those kinds of topics to be completely on-topic and valid, removing the reports. All of the relevant Steamworks pages aimed at publishers (eg Steam Community) are publicly available and are really enough to blame Valve for the whole state of things.

Even if a publisher opts-out of Valve moderation, they don’t have the tools to deal with sockpuppets or organized attacks, and being banned from one game forum just means those same accounts move elsewhere. Valve could absolutely deal with it by doing community-wide bans, but they don’t.