Because they don't have enough personality, apparently.

http://uk.ign.com/articles/2012/08/15/how-fir...growing-up

Motherfucker. I am so raged by this i can't even explain it properly in words. C/P of my comment on this from another forum:

What a crock of shit. FPS games were, for the most part, never plot or character driven, you measured their quality by how fun the wanton carnage is and how appealing the aesthetics (and gameplay mechanics, if we're talking competetive multiplayer) are. And that was perfectly fine. That was the god-damned point. Everything else is extra flavour which can, but doesn't necessarily have to, make the experience any more enjoyable. What the hell do i care if the electronic proxy i use to blow shit up is in emotional turmoil? Or has some complex motivations behind killing bad guy #million which affects Joe the NPC's moodometer, and that will decide whether or not he'll give him a blowjob in an alleyway. Fucksakes.

Obviously you can switch that brainwave off for games like Deus Ex and whatnot, but the entire genre was built upon arcade shooters, and now it seems the cinematic bullshit is slowly but inevitably making them extinct. Ooh, terrorists killing people at a terminal, that's not a juvenile grab at shock value, it's the genre growing up. Ooh, the protagonist is a basket case, i really need to know that to enjoy shooting some faggot in the head. Yeah right. Fuck that.