I think the point of the sub-parent was that some nerds never got a chance to mature. This is not meant to defend such behavior.

I would change your statement to read "never chose to mature" rather than "never got a chance to mature."

If you spend your formative years not taking advantage of the opportunities that exist, I have trouble mustering sympathy. (And like I said elsewhere in this thread, I certainly did that until the middle of high school. It's not easy to break out of it, but the only one who can is you.)

Every single rejection from a girl in high school or a woman after that is a chance to mature. In fact, it's a nearly-spoon-fed opportunity to mature.

Anyone that doesn’t mature at least somewhat from such scenarios is actively choosing not to. Maybe not consciously, but they are making the decision to resent and blame, rather than regret and find out why they got rejected.

There is no why. Nerds think there should be an actionable reason, and that's part of the problem. It's just how she feels, and even she probably doesn't understand it. We accumulate years of damage from bad advice because better advice (rejections are too random to take personally, so forget your big doomed crushes, improve your odds where you can, and try everybody) is somewhat dehumanizing.