There is activity because people choose to be active. To no do so is apathy, or to not know what is occurring here. We don't have a community if people within the community aren't doing anything, and it's as much of a problem on our end as it is for the members who are still here.
We may be a Halo-centric forum, but Halo isn't our only gaming interest. There's plenty to talk about and do besides everything Halo (which is essential, because 343 is completely inept at keeping the interest up for Halo). I know I'm one to talk since I've stopped doing Polls & News, but unfortunately for allot of us Staff our lives are constantly taking up most of our time. We were lucky in our earlier days because we had allot of younger folk with less responsibilities who could go insane on here 24/7 (which used to include me), but that's not the case anymore.
Anyway, what I'm getting at is that if you want an active community don't expect us to do everything to make it active. The thing that will actually succeed in making this community active is... well, for everyone to pitch in and get active. Care. Do something about it. Everything will change then.
Side note: I think a large part of why this site is inactive is because the barrier to actually do something here is too great to get over. For example, let's say you want to play VR or something. First you have to move all the furniture, set up the headset, turn the game on, etc. There's too many steps, and people want to talk NOW. That's why Discord is so convenient, because the barrier to talk is thinner. Like, the chat in Discord is 110% better than the Shoutbox :/