Actually, there are two or three things.
1. Some kids may be "essentially" (for lack of a better word) gay. Irving Bieber's work in the 1950's with numbers of gays and "conversion therapy", in which he tried to intervene with psychotherapy to help homosexuals work out whatever issues might have been contributing to their homosexuality, found that there was a fraction that responded to psychotherapy (confuting the modern gay psychiatrists, who promote essentialism as the "official" line of the American Psychiatric Association and American Psychological Association), and another fraction, about a third, that didn't respond at all, who might be denominated "essential", or "biological", gays.
2. Sexual ingenues can be educated to homosexuality. Gays brag about it in private, but assert the opposite on the record when the debate is on.
3. Some people don't have a solid psychological background (a.k.a. a "good upbringing") and so are available for homosexuality........or whatever you've got.
For a while after the fall of sound psychiatry on the subject in 1972, the Diagnostic and Statistical Manual's third edition (DSM-III) carried a term, "ego-dystonic homosexuality", which meant homosexuality that caused suffering to the patient. This category has since been eliminated by the gay guardians of PC on the subject, the rationale being offered that, if only society would stop persecuting gays, they wouldn't suffer so. Substitute the words "murderers", "felons", "firebugs", "dipsomaniacs", or your other favorite outgroup here, and you can readily see where their logic leads -- and what I think of it.