I think you're ignoring the growth metrics of players who don't want intelligent AI. People are happy in their mediocrity, all they care about is the illusion.
Any good AI is just an illusion, anyway. I can't think of any games in which the AI actually did much reacting. Nearly any FPS is just whack-a-mole.
But I'm not saying AI can't be important, I'm saying that the value you get for significant time put into AI development is way, way, way behind the value you get for significant graphics development, so you get better graphics. Considering even Crysis 2 threads here have had people complaining about the graphics not being advanced enough I'd say it's pretty clear why so much effort goes into that area while AI lags far behind.