In general, we expect all threads to roughly stay on topic and encourage this as a matter of policy, not just community threads. Community threads present a couple of unique issues. The first is accessibility: when new players pick up the game, and want to talk about it on GAF, they often turn to the community threads. Entering a topic about the game they want to talk about and seeing it filled with Bloodborn boss discussion and other random topics can be off-putting (and we've seen a few folks come through these threads recently and make posts along the lines of, "Is this community always like this?" That's not a good thing.) As a side note, Destiny is still selling; I poked into the PAL sales thread and saw it was
#10 on the combined platform charts this week, 8+ months from release. Still plenty of new members coming in.
The other has to do with how communities come together and can become insular over time. This is again related to accessibility, but the side effects can be more corrosive to the forum as a whole. Close knit communities - especially gaming communities - sometimes take on this attitude that they are some kind of offshoot from GAF ,with their own identity. DestinyGAF is a thing, but the GAF part is just as important as the Destiny part. We see this from time to time when someone makes a disparaging post about those "gaming side threads". As in god, those gaming threads are awful, let's stay in here where it's safe and warm. (I've made some posts discouraging this in the past.) This kind of insularity can also be unwelcoming for new players wanting to come in. When coupled with a community that is also going wildly off topic with frequency, you have a thread that is very unwelcoming to new people, and which is no longer serving the purpose for which the thread was created: to be a place in which all active players of a game can feel welcome posting. We've seen some communities turn actively hostile to new members, especially if they come in with differing views. Our moderation policies are generally in place to prevent this kind of thing, but it's tough since there are a LOT of active community threads, but limited moderators. We do what we can.
As to leaving more active threads on the main forum, it has been discussed. The original issue the Community forum was intended to solve was, allowing the front page of the forum (which is the most widely used view on GAF) to be populated by current news topics, and so serve as a source for discussion of current gaming news. As the forum grew and there were enough members to keep a large number of OT's active at once, it was crowding out other threads and diluting that purpose. After some iteration, the current policy evolved: gaming OT's move to Community after one month, regardless of how active they are. This solves a few issues: 1) we don't need to pick and choose what threads are active enough to keep around, and 2) it sets the expectation that the Community forum is not a "junior" forum to Gaming. We don't want Community to feel like a dumping ground for unpopular or old OT's, but rather a part of GAF with a specific purpose. Imagine how some communities would feel snubbed somehow if there were not left in Gaming, but others were. (It would be a big thing we'd have to deal with.)
Hope that helps clarify things. Feel free to PM with any other moderation questions.