Misogynistic males are the most sexually successful and popular with women. Male loneliness is largely felt by weak, soft, and highly inhibited males (ie., the ones who don't actually cause any problems for women). I think women tend to assume the outgoing and good looking men they interact with are representative of all males. It's a kind of rationalization based on the just world fallacy. Only the bad men can end up lonely and isolated as a just deserts for their awful behavior. Guys who struggle romantically aren't feeling blowback from their own bad behavior or even of other men so much as they are dealing with a lack of good looks or natural masculine charisma.

It's also worth pointing out that loneliness does not just limit itself to sex or romance. It also includes platonic friendship and maintaining a relationship with biological family. If men aren't even able to make friends with other (presumably sexist) men then something bigger is happening. I'd point out one major epidemic in loneliness is the one experienced by the very elderly (people in their 70s and beyond). I don't think this is some kind of cosmic justice for the ills that older generations inflicted on younger ones. It's more to do with naturalistic reasons (all your friends and older family dying off) and social ones (lack of social networking opportunities for the retired in an increasingly secular world).

I also want to point out that top comment where women say "man aren't enough lonely" or "they deserve it" ger thousands of likes. We are still in the minority, even if growing. Most normies have an opinion closer to the "men bad" narrative.