One reason among many may be that trying to get a head-shot, or even attempting any kind of accuracy during a fight using a game-pad must be about as easy and intuitive as trying to pick up a pencil off the floor using your butt-cheeks.
Lmao, head shots are gravy is this game on the 360!!!!! Maybe poor hand eye coordination with joy sticks put u off but just notice this game was made for us console players... I even have a Mack ass gaming computer but this game is not for that unless u like to mod, in which I do not