Perhaps the more striking point is that Reach was still at #6 two years after release, right before Halo 4 transitioned population out of it. Or that Halo 3 spent its entire life near the top; it wasn't until MW2's release in late 2009 that Halo 3 was finally kept out of the #1 spot for good.
I'm not going to pretend to be terribly bothered by this, though. I get that saying stuff like this can easily put me into "horrible person" territory, but I'm happy that a Halo game whose direction I don't like doesn't have the legendary momentum of its predecessors. It means change toward a direction I do like is more likely. Microsoft isn't commanding my attention very well right now, but if they decide to change that, great. I'm still sort of listening.