Quality comes in many forms.
Take Arkham City for example. It's a GREAT game with a great story and are excellent in almost every aspect, but after you completed it, finished all the challenges etc. you are going to move on to a new game, maybe picking it up again a few months later.
You see, this is the point where games like Modern Warfare and Battlefield shine. Those series excel in providing a lot of entertainment value with a VERY long lifetime, which is more than most other games can claim. Arkham City is a great experience, but for most people it's not gonna last much longer after they've completed it. Modern Warfare and Battlefield, by contrast, are games that people are going to play almost every day for a very very long time into the future. Over time, they simply provide more entertainment value.
It's the same thing as when Counter-Strike became popular 10 years ago. Counter-Strike wasn't a revolution in itself. It had limited content (initially) and simple gameplay, but at the end of the day it was god damned entertaining and very cheap. To play Counter-Strike, i had to pay $15 bucks for Half-Life, and i played Counter-Strike for 5 years. I doubt there is ever going to be a game again that will ever provide me with so much entertainment for so little a price (i played WoW for just as long, but that cost me a monthly fee, and they had to provide new content all the time to keep me interested).
Games that excel at long-term entertainment value generally sell better than games that don't.
