I doubt the upper class consciously tries to keep the lower classes stuck in poverty.

There are so many factors here the article doesn't touch on. Such as men's biological desire to maximize sexual partners, women's biological desire to maximize quality of and support for offspring, and cultural variation of expectations among all classes.

In my circle most of us were raised by parents in unhappy marriages. (Often for religious reasons.) The few happy marriages appeared surreal like some fake Hollywood production. So the same norms that keep families 'intact' can have a lot of unhealthily effects.

There's also less of a ramp or ladder for men who do want to support the family to commit to such an obligation confidently.