We only review forum posts and threads that receive flags, so that limits what forum threads are subject to closure.
I usually only close down forum threads that have a high number of valid forum flags on recent posts in a short amount of time. My goal in that is to prevent more people from getting forum bans for piling on in an immediate argument.
If you run into a thread that you think is unnecessarily hostile, feel free to flag the most recent post as "other," explain that you'd like this reviewed for closure, and we'll be happy to take a look.
If you have any other questions about moderation policy or HubPages in general, please feel free to contact us: http://hubpages.com/contact_us