I've never really cared about rank though. Lack of incentive, yes. But I'm at a loss as to what the incentive was in the first place.
There are definitely other factors. A lot of it has to do with the way information about how you're playing is fed to you. Even though you might not care about ranks, winning or losing is still a driving factor in how much you might enjoy what you're doing.
Winning feels less important in Halo 4 than it ever has. It, like Call of Duty, has become about the individual's progress rather than the success of the team. How many +WHATEVER did
you get to fill
your bar? The postgame report doesn't display final team scores. A small exp bonus for winning isn't enough to drive teamwork and excitement. I already filled my bar, so I stopped playing and stopped paying for Xbox Live. I didn't feel driven to play anymore.
Even though I felt entirely betrayed by Halo 4's multiplayer, I was enough of a fan of the franchise to give the entire multiplayer progression a chance. I reached the end and lost all desire to play, a clear indicator that the core game couldn't find a way to make me care.