It's not for lack of trying it. I realized every time I did it, even if I was attracted to the guy, I just wanted it to be over. Had I known asexuality was not a binary thing, I probably would have identified as such sooner.
Since I've gotten older, I have come to realize that I am mostly asexual. I am not romantically attracted to either sex really. Hard to explain. I have attraction to female genitalia but could never be romantically attracted to one. Same goes with men on the romantic level. However, I am much less attracted to interacting with male genitalia than female but visually enjoy looking at x-large penises.
As is well-known the site, I enjoy chunky lesbian porn, some straight big dick porn, and, once in a while solo jack-off scenes. Watching gay porn is rare but happens.