A reason to shut down the forum entirely instead of leaving it in its current state is that low quality posts made by randos here can hurt the reputation of the forum and the people & organizations that were at one time or another affiliated with it. See e.g. this farewell that someone linked to on SlateStarCodex. There places online like the /r/SneerClub subreddit where people will post something that one particular Less Wrong user said and make fun of it, which tarnishes the reputation of the site in general. Banning Lumifer and VoiceOfRa would help a little in the short term, but running a quality online forum requires ongoing maintenance.