We all know the main determining factor in whether someone gets CoD or not: How many of your friends will be playing it?
At least for me personally, CoD isn't the type of game I enjoy playing by myself. I got a lot of enjoyment playing with friends(albeit it can still be pretty frustrating), and usually whether or not I got the next CoD depends on how many people I knew were going to be playing it. Even if I have Black Ops II and I'm still enjoying it when MW3 came out... there's no point playing it by myself when everyone I know is playing MW3.
That pretty much sums up my experience with the CoD franchise. It is a horrible, horrible domino effect.