I would posit that women's hypergamy is a constant and that the girls you describe simply have had zero cultural messaging that would influence them in the direction of curbing it. Prior generations had more messaging in that regard, even millenials had some lingering societal sentiments filtering in that "hey, sleeping around and being disloyal at the first opportunity isn't a good thing". Gen Z? I doubt they've even heard of such concepts growing up, so the raw female instinct to always ditch your man for a better one is now manifesting in full.

But yeah, shit is absolutely fucked and I suspect there will be entire generations ruined before the issue starts being addressed.