At least in gay porn it's clear both participants are having a good time. Lots of straight porn features chicks who seem bored, turned off, or just not into the scene.
To make matters worse, very few pornstars actually look at the dick. I like it when they stare at the dick, it's awesome. The guy is always staring at the chick's ass/boobs/whatever, so they should return the favor and look at the cock.