In a classic agrarian economy, having a spouse and making children works out -- more children = more hands = more work done = more food or more product to market.
In a modern "pure" capitalist industrial/service economy, the economic model doesn't pay for the cost of the reproduction of the labour it depends on. So not a surprise when people do the same cost-benefit analysis for themselves and choose (or are forced) to have no children, and to not bother with marriage as a result.
The no-children "choice" often also ends up with no partner -- married or not. I personally knew several women in their late 30s and 40s who ended up leaving partners or leaving the dating scene because the men they were finding were not interested in or capable of being fathers. On an aggregate scale this adds up to a phenomenon.
Some advanced capitalist nations have gotten around this through high immigration rates. Others are attempting to get around it with debt to finance social programs or stimulus etc. In both cases it's really just "shooting the puck down the ice" so to speak. The next generation or the one after has to deal with the problem.
Perhaps they weren’t interested in the challenge and issues that come with a woman in her late 30s and early 40s attempting to conceive a natural healthy baby while risking her own life as well. I bet these men in a similar age range of these women are looking for partners and potential mothers in their 20s and early 30s. There’s less of chance of issues and conceiving is much much easier as the women aren’t premenopausal.