It comes down to Long Term Security and Reproduction. Protection, Provisioning, and Parental Investment vs Arousal. Seed vs Need. When it comes to the beta bucks side of Hypergamy, women are inherently security seeking. This is more transactional in nature, and is pretty common. But due to increased living standards and technology, we're more secure than we've ever been. Women still need it, but the nature of it has changed, and women don't want it as early or as often. They basically don't want to get married or in a serious commitment as early as they used to. For the Alpha F*cks side of things, the Sexual Marketplace has opened up since Hormonal Birth Control became legal in the 1960's. It reduced the cost of sex for women, and decoupled sex from relationships.
When it comes to relationships, specifically marriage and long-term relationships and starting families, guys used to hold the key to that, and it was mostly out of necessity due to survival reasons. That's not as much of an issue anymore for women, at least perceptually. Hormonal Birth Control effectively put reproduction in women's hands, so if you want to get married or start a family with a woman, you're taking a bigger risk, and have to jump through more hurdles to do it. As for casual sex, access is way easier.
To bring it back full circle, women control access to sex, while men control access to relationships. Women's primary agency is their sexuality and fertility. Men's primary agency is Protection, Provisioning, and Parental Investment, Competency, or their Burden of Performance, whatever you want to call it. The only difference now is women can have more sex without worrying about unplanned pregnancies, and we get married less, have less babies, but more casual sex.
While my opinion on women controlling access to sex and men controlling access to relationships remains the same, there's not as much of a hurry to have families, if at all. Basically, it's just harder to start a family and have a lot of kids because women don't want to get married or have families as often anymore unless you're a top shelf man. For the right guys, they'll break their own rules, but generally starting a family and trying to do anything serious has become tougher.