This is actually tied to the whole "gender pay gap" myth as well. Women do as a whole make less than men, but it's not because of discrimination. It's because women are far more likely then men to choose to leave their careers early, work fewer hours, want to take time off to stay with kids, etc.

It's very common for the "womyn power" careerist types to reach their late 30s and early 40s and decide that the whole "queen of a man's world" thing really isn't all that enjoyable, try to settle down as a homemaker, and realize that despite what they were told by their sociology professor in college, being a stay at home mom is a hell of a lot more enjoyable and fulfilling than trying to work 60 hour weeks to become a Senior VP. Almost as if they're wired that way...

It's the flip side of the coin where a hell of a lot of stay at home dads end up feeling worthless, unaccomplished, lethargic, and like they failed at something though they can't quite put their finger on what exactly.

Obviously nothing is 100% and you will always find outliers for everything, women who do the career thing their whole lives and love every second, men who just raise their kids without working and feel like it's the most rewarding thing they could have done. But as a whole men are wired to find the greatest sense of fulfillment and accomplishment when they are out achieving external success, and women as a whole find the greatest sense of accomplishment from raising and taking care of families.

And a great number of either who try to buck the trend and do the thing that the other gender is more apt to do end up feeling like something is missing from their lives. It's like their genes are protesting their conscious choices.