Infinity Ward and Activision started to not get along anymore. They just got too big. A few very important people at Infinity Ward was "dismissed", and several other very important people followed their bosses.
Infinity Ward, in it's hayday, with the release of Modern Warfare and MW2, would have been amazing. No compromises on the games. But if Inifinty Ward would do it, would they keep going with it. If RC2 was as popular as the first Modern Warfare, would they make more? would they kill it? would they stop innovating like they did with the MW series?
Would you rather have someone like Infinity Ward make an RC2, and an RC3, possibly an RC4, and possibly destroy it all with oversaturation of the same thing? Or would you rather have it go the way of a Halo movie? Not want it to happen, because you don't want them to screw it up.
The very existence of flamethrowers proves that some time, somewhere, someone said to themselves, "You know, I want to set those people over there on fire, but I'm just not close enough to get the job done." -George Carlin