Ooh, I read a thing about this. There's been studies on this that tracked eye movement and brain activity. Most straight men when watching porn watch the woman, while gay men focus on men. As you'd expect right.
However, both straight and gay women tend to look at and get more excited by the woman in the scene.
The thinking is that while men use porn as a strictly visual aid, "woman is hot, makes me horny" etc, women are more interested in using it to stimulate the imagination, imagining themselves in place of the woman in the scene.
This apparently explained why a lot of straight women enjoy lesbian porn. A lot of straight porn is about male pleasure, blowjob, man rails woman, more blowjob, cum shot. Not even a fake orgasm for the woman.
Lesbian porn, even when produced for the male gaze, is more about the woman's pleasure. So therefore a lot of straight women preferred it, as it was more enjoyable to imagine themselves in the place of one of the women.
Obviously it's just theory and trends and won't be true of all men and women, but was an interesting read.