That's an interesting take, Benny. It sounds like an evo-psych theory that I'm not quite sold on, but I appreciate you sharing that idea nonetheless. Tbh, I actually think it's a bit simpler than that; I think that both women and men like stability. A man who expresses his emotions by, for example, raging and going on bitter tirades — bad news. Anger issues can be dangerous. Likewise, a man who needs but refuses to seek therapy, expecting to use his partner for therapy instead — also bad news. Because he's not taking real responsibility for himself. (Any woman who behaved in these ways would be bad news also. I hope that goes without saying.)
These kinds of people are unstable. But the problem isn't that they have ups and downs of emotions: the problem is that they are handling them in unhealthy ways. By contrast, a man who is kind and emotionally intelligent, who's capable of expressing all kinds of feelings non-abusively, and who recognizes when he has (and follows up on) a need to seek professional help — THOSE are the truly stable guys. Not the stoics. Men who aren't afraid of emotions are sexy, because they are very obviously the ones who can weather life's storms.
In any case, I didn't mean to say so much here, but I guess I'd wrap up like this:
There are tons of people of both genders who are unskilled at knowing how to express vulnerability, and tons of people who are unskilled at responding to it. My guess is that the women (and men) who pick stoic partners are doing so because those are the kind of adults they saw growing up: parents who were inept at displaying/ talking in healthy ways about emotions. It makes sense that those people would, then, have absolutely zero clue HOW to respond to a partner who began to show their emotional side. I agree with you: it's not that they don't care. It's that they literally never learned the skills for dealing with that. But is it about an ancient, evolutionary drive for "security" and being provided for? Not at all. It's something much more recent than that, and nothing that a psychologist can't fix. ;)
