Because when I hear "Happy", I think of all the wonderful adventures COD has to offer.
Uhm, no offense, bro, but, I don't really see the relation of Kendrick Lamar being on a game such as CoD. I mean, if he would perhaps rap and then add some explicit words, fast beats, that would also be acceptable, but if he's just gonna perform another "Happy"-esque song, no thanks. I would love to hear some bands perform though, or perhaps some Daft Punk with hardcore mixes. I mean, it's Advanced Warfare. Imagine combining both. Daft Punk+metal music = Totally Awesome.