I have thought about this a lot throughout my life (I'm 62), because my gay desires have been so powerful for most of my life. I've come to the conclusion that our genetics plays a huge role in it. I really believe in the gay gene. Some people are just born having desire for only the same sex. Others may have both same and opposite sex desires, but one becomes dominant over another for different periods of one's life. And certainly our homosexual desires are strongly affected, in a negative way, by the homophobic society we live in. Without that, I believe homosexuality and bisexuality would be far more rampant. And events in our life, especially in childhood, can also affect what dominates our desires. For example, I'm a guy who has been hurt by a lot of girls and women (with countless rejections) throughout my life, starting with my mother who beat me viciously and continuously from a toddler to my midteens, leading me to prefer men in my sexuality.
But mostly I just know that I was born gay, and I've just been fighting it all my life because of my internalized homophobia. Internalized homophobia is huge in everybody who has any homosexual desires, causing us to constantly repress those same sex desires that desperately want to manifest and be accepted. I believe that's why when a guy finally comes out to himself he goes absolutely wild with sex with other guys and with many partners. It's like the cork being blown off a highly pressurized bottle. I believe if the male body was sexualized as much as the female body in media, half our male population would be gay, and 50% of the other half would be bi. The same doesn't seem to work with women and lesbianism though: I don't know why, since women are inundated with the sexualized female form as much as men are. But if the cock and male ass were as revered in the countless types of media in our society as women's breasts and ass are, man on man sex would be happening everywhere!
Most of all I've come to believe that same sex desires are completely natural. It even makes a lot of sense, since people spend most of their time with others of the same sex. So it's completely natural to desire sex with people you socialize most with. Guys are also sexually built very different from girls, having a far greater sex drive on average, right up until their 80s, that makes monogamy with a woman ridiculous. It makes far greater sense for the ever horny men to be playing with other horny men. And of course, at least for guys, there is the reality that the erect cock is the most beautiful thing in the universe. It's why there have been societies throughout the ages that have worshipped the phallos, symbolic of virility and strength, very attractive qualities. In addition, we come to love our own cock very much, so of course it's very natural to love other cocks.
And the ultimate reason that we love cock, male ass and everything else gay so much is because we have infinite familiarity with loving them in our infinite past lives--if you're one who believes in reincarnation. That's why at 8 years of age, even before I heard of the word sex, let alone seen any pictures of men & women or men & men engaging in different sexual acts, I knew everything about sucking my 8 year old best friend's cock, rimming his asshole, and trying to push my soft cockhead into his asshole. Our hot sexual affair continued until we were 13 for God's sake, long before we ever had sex with females!