I suspect that one reason for this is simply that marriage is delayed too much. A woman’s peak childbearing years are 16-32. Naturally, a woman has an urge to have children during those years. In other words, you aren’t going to fix this and also have a median age of marriage at 29 for women. A lot of “hypergamy” is driven by what amounts to genetic selection, or “looks.” What’s the point of genetic selection? Pleasure in the moment? In part, but also, of course, genetic selection. Women have these babies because they want to have the babies of the men they have genetically selected for.
Marriage and monogamy are common to all successful civilizations. It is basically identical in China and in Spain, for thousands of years. When marriage and monogamy weaken, we have a return of an earlier, animalistic simple genetic selection model. This is incompatible with civilization, because, if it was compatible, we would have seen some evidence of it, in the last 5000 years, and we do not.
Cornerstone 