Same reason people hate on COD, it's a game they simply do not like.
There's more to it than that. Some people just like to put down games that others like, and they say pretentious and really dick things about the fans that do like it.
I can't stand pretentious douchebags that do that. And it sucks because some people that I normally like act that way, and COD really brings it out of them. --- There's no sensation to compare with this Suspended animation, a state of bliss