User blog comment:Damac1214/Why Call of Duty is Call of Duty, Fallout is Fallout, Halo is Halo, and that they aren't going to be changing anytime soon/@comment-5115149-20130316082509/@comment-1187559-20130316164855

Activision wouldn't tell Treyarch or IW to pit Frostbite into their game because they're just the publisher. While they might rush the devs they don't tell them what they can and can't have. Also they wouldn't use Frostbyte since that would radically change the game, and I don't mean this from a players perspective, but a programmers, all of the game would have to be reworked in order to function with the new engine.