We dont know that.
Unmarried lower income people are more likely to have criminal record, more likely to have mental health issues, more likely to be the ones having hard time to keep jobs, more likely to have drugs related issues. Among women, those who got pregnant before marriage and much harder time to get any money and also are less interesting romance target for guys.
People nowdays see marriage as something you do once you are set by your standars and that strongly biases who marry.
https://www.stlouisfed.org/publications/in-the-balance/2018/...
The fact that a college educated person earns less than what you claim is a mentally unwell, non job having drug addict is sad but no all to unobvious. Why would you think a teaching degree or psych degree major would earn more over their lifetime than a plumber or construction worker.
The fact is single women benefit the most financially from marriage since single uneducated and college educated women have a much higher than average poverty rate.
People with real issues, whether mental or criminal or sick etcetc both don't marry and have significantly smaller income. People with issues divorce more often and have smaller income too.