Some of the gap in income & wealth is a function of age. The dirty little secret of the wealth gap is age. The average boomer household is loaded. The average millenial is on a boomer's couch. And older folks tend to be married. Younger tend not to be married, seeing mostly risks and little or no reward, what with the stigma of shacking up and having sex and even babies outside of marriage having been obliterated.
But....
Here's what you don't grasp fully unless or until it happens to you: marriage protects the weaker partner. You might know which one you are today. But you don't know which one you'll be tomorrow or 10, 15 or 30 years from now..
A case study of my own marriage would show a hard worker, 2 full time job working stiff who fell for a work part time, school part time, idealist with an itch to travel and have all the finer things. Yes, it was saver (him) and lover of luxury (me). We married. Eventually, he became disabled. 30 years after promising forever, I now out earn him by something north of 50:1. There is no crystal ball. If we had not married, I'd have zero obligation to take care of him. He'd be the government's problem and a pauper. My personal networth right now could be higher. But 25 years ago, it looked like it tilted the other direction. It seemed like he'd have been Mr. Success and I was just along for the ride.
The fact that I have someone dependent upon me does make me work harder to provide. There are economies of scale, a balance of temperaments and a complementary skill set in the home, all of which make us richer, not just in dollars but definitely in those, too, in our case.
OT: regarding Murray's research about racial differences in IQ scores, don't draw the wrong conclusion. IQ tests themselves are biased. IQ is only one measure and it is suggestive of something the way that BMI is suggestive. By itself it means little.