I think you have the right of it, but not completely. Men feel romantic loneliness differently from platonic loneliness because it has a couple layers attached to it: failing to live up to being a man (esteem), failing to live up to being a man (identity), and lacking the one relationship where you're supposed to be able to talk about your feelings (lol, but in a sad way).

This is very much a gender expectations issue, an issue of society rather than men (or women, obviously) in terms of blame. But men are nonetheless pressured in this way at all levels. Attraction is just one relevant aspect, as it places a higher/lower difficulty on the romantic relationship and on esteem. But I think you're right that a huge part of the problem is a broader social decline of community and shared purpose, particularly for men in their platonic relationships (though far from exclusively).

Much of the difference between genders stems from the enculturation of men interacting with the decline in opportunities. I find platonic relationships far, far easier in shared physical spaces, and outside of them, I struggle to go out of my way to plan group activities, particularly when money and time are in short supply and with friends moving everywhere for jobs. I think there's a personality and behavior difference here, given the current condition of society, such that women are more likely to do what's required for relationships to work well where men do not (and this snowballs). You might notice this is also an issue romantically, lol. It affects women a great deal, as I think you were saying. And if men are struggling in one type of relationship, it affects the other.

Please note that I'm not using the typical "blame" paradigm here. Just speaking of behavior... and all behavior is caused. People can't simply start doing all the good behaviors, so to speak. If they could, they would be already, and therapy can only shift so much inertia. Plus, it's not like they have a crew to guide them along. Instead, the environment (in the broadest sense) needs to be made conducive to the behaviors people need. Or at least we should slow the steady decline in environmental quality...

Unfortunately, we're setting ourselves up to make this and all related issues far worse over the next generation. Much of the fundamental environmental problem is economic in nature, with labor power dropping generation by generation, issues like the decline of third spaces, and a variety of knock-on effects. Subs like this one will probably get more common, and the form of radicalization it often hints at will only contribute to the social problems that cause it. Both for the individuals involved and in society more broadly. I don't have a solution that's going to be embraced enough to matter. We just can't blame women. And we can't blame men. The problem has a larger scope.