Well not to be all

about it but I think there is a value in breaking out some specific phenomena from the broad label of "gay men", one that directly related to troons. There was a
study in 2011 that surveyed 25,000 MSM (gay and bisexual men, but specifically identified by whether they have regular sexual contact with men) that found that only about 36% of them reported any type of anal sexual contact or stimulation. Oral sex and mutual masturbation were far more common.
There is unquestionably a direct erotic stimulus possible from prostate massage (as our consistently oversharing fellow kiwi
@The Un-Clit talked about above), but anal sex in gay relationship is more a culturally normalized thing than a defining desire in gay men (many of whom are only tops if they engage in anal sex of any kind at all).
There do seem to be distinct behavioral tendencies in gay men, that while they often co-occur, are not universally present together. One strong seperation I see is between androphilia (a sexual attraction to masculine sexual characteristics) and a desire for a submissive posture in sexual situations. And as we see in these trans threads, many AGP who otherwise report exclusively a sexual attraction to women begin actively fantasizing about being fucked by a man without really caring who that man might be. It's not something I was really considering before really reading these threads, but I've been wondering if there are essentially different kinds of gay, one type of which also may troon out because the desire is not so much for men themselves, but submission to them. Probably there are some innate neurological predispositions, but there's likely an environmental or socialization aspect to that desire.
I just wonder when I think about incels and autists like Chris who showed insecurity or even cowardice with being the sort of classically male active pursuer in relationships, and wonder if there isn't some causal link there. A sort of rejection or sense of inadequacy with normal male sexual dynamics in heterosexual relationships that lead to essentially a regret in being male, and a desire to adopt the other half of the equation.