It's the Tribute Hall boons.Man wtf happened to Menagerie? I'm either joining games already in progress or always short by one or two people. Also raid banners are now dead because everyone is short on resources to buy them.
People have to load into Menagerie get 20 kills. But they're only there for that bounty, and after it's fulfilled there's no incentive for them to stay unless they want a chest. So they don't. Same with Strikes. If you see people leave mid Strike, this is why. Bungie once again not thinking things through.