It's very easy to find straight porn focused on female pleasure online. And if you look in the comments of such videos there are women saying that they enjoyed it. However most women would still prefer to watch lesbian porn.
I'm sorry but all the justifications from women who identify as straight on why they watch lesbian porn just seem like mental gymnastics to me. If a person is aroused by the same gender (let alone if they prefer watching that) they are not straight. If they aren't attracted to women in real life they are probably repressing the part of themselves that are attracted to the same gender because of societal conditioning in my opinion.
People can watch what they want and identify as what they want. But me personally I want to be with a woman who is truly straight.
I think your issue is that you can't shift your focus in porn. Straight women can focus on the pleasure the "bottom" (or whichever woman is the pleasure self-insert) is feeling and expressing, and use that to fantasize, completely cutting the "top" out of the picture. Many women have a more naturally fantasy-based mind, while men don't.
I, despite not being a woman, find it easy to "block out" people in porn if needed and focus on the part that I want to gain from it. The fact that you go flaccid the second you see a man on screen, even if the point of said man is to be your self-insert, boggles my mind. Sounds like you have inherent empathy issues to me.
Also... women are individuals. Some women comment under rape roleplays about how much they enjoy it. Just because "women comment under it liking it" doesn't mean it's female pleasure centered. Also, plenty of women themselves have been brainwashed to not know what true female pleasure is. As I stated before, many are still obsessed with penis size and male physique. It's a societal problem.