It's well known that women very rarely date/marry below their level, which means an extremely narrow dating pool for these women at the top, not matched by their male peers. The same is simply not true for men. And if you're a man thinking of bucking this trend, you're putting yourself in a pretty risky place.
And it must be intensely frustrating for them to find it when they correctly surmise that they're running out of time (for having kids), after no one ever offering this wisdom before they had to suffer the consequences. I'm watching my siblings and my wife's siblings, along with many coworkers, suffer in this way, and it seems agonizing.