I don't think this is a universal fact, so much as a result of the way that dating culture has played out over the last few decades.

If you read the work of earlier sexual reformers, particularly Wilhelm Reich, who wrote "Sexual Revolution" in the 1930s (yes, that one), then you instead find dreams of new ways of living together, with sexual freedom going hand-in-hand with the total abolition of the nuclear family, etc.

Instead, we've become more isolated in societal terms, and more dependent on commodifying ourselves and others (particular in terms of image) in order to attain our social and physical pleasures. It is the result of this shift--isolation and atomization, not freedom qua freedom--that we see the problems discussed here.

I'd argue that most men that won't have sex probably have some character issues they need to work out personally, or otherwise need to develop into somebody interesting. Dopamine hits from other places are more easy to come by, so it wouldn't surprise me that they just don't care enough, relative to their peers.