Among animal populations that are stressed from over-population, including our own, you would expect some of those animals to start desiring same sex partners and some to have no desire at all. It has been a long time since I have seen studies on this, so I have nothing to point to, but it is easy to imagine how that might be evolutionarily viable behaviour for an entire species.
I wonder how many of the four percent are closeted homosexuals. It wasn’t until the seventies that homosexuality was dropped as a disorder by the Diagnostic and Statistical Manual of Mental Disorders. Previously it was described as “paraphilia”, “sexual orientation disturbance”, and “ego-dystonic sexuality”. I also wonder how many of the four percent are unacknowledged asexuals feeling the pressure to perform. I see “hypoactive sexual desire disorder” in this article and think of course these men are depressed after sex. “Yes” has no meaning if “no” is not an option, even if that “yes” or “no” dynamic has been internalised through cultural expectations.