Be into it for whatever reason you want to be, but lesbian porn probably has the benefit of women being generally more ionate than males do (something something primal breeding desire) so we see it as more attractive than two guys going at it. A tangent to that, you can have two guys going at it but unless one is really feminine (and thereby submissive and cute-ish), it kind of boils down to the top guy exerting his desire on the bottom guy with less proof of ion being involved. Not to say it isn't there, just a bit more difficult to prove.
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Or something like that. I'm no phycologist