The issue is that there's no objectivity here. Are these women actually sad because they truly wanted to experience motherhood, or is it more because of pressure (even unconscious pressure) from family and friends to have kids? Or just the built-in feelings due to upbringing that having kids is "just what you're supposed to do".

I wonder, though, if these same women did have kids, and sacrificed their career for it, would they look back and have regrets in that regard, too.

So maybe it's just... given a multitude of options where we can't choose them all, perhaps humans will just naturally have some regrets around the path(s) not taken?

As counterpoint, I know women in their 40s and older who are very pleased with their decision to not have kids.