You are being suspiciously simplistic here. Needing to work hard to get a bride is one of the things that most vitally supports a culture of work ethic among men. Very few other things seem to have as big an impact. Most Fields medalists probably didn't work hard primarily because they wanted to attract a wife, though I bet many of them actually did. But the culture of work ethic being normative for men certainly seems vital to supporting their efforts!

To summarize:

1. Men can attract women with hard work (note not about money per se, it can be status)

2. The above is one of the strongest factors that contributes to a cultural expectation of hard work being normative for men

3. This has strong impact on the output of high performers

If it wasn't for the ruthless class segregation in the modern West, where people with high genetic potential are quickly identified and sorted by the academic system into subcultures where men attracting mates with hard work still happens things would probably be pretty bad. If you don't think this happens I would direct you to Charles Murray's book Drifting Appart. And even the upper classes are drifting away from this model, this looks to me like a social disaster in the making. Things will overall still get better due to other factors in the medium run, but the opportunity costs are terrible. (<_<)

I remember one ha-ha-only-serious from my mathematical days: Sex is just a sublimation of the urge to mathematics. (And it's long been observed that even among young mathematicians, their output falls off dramatically if and when they marry).