They simply decided what they valued more between later academic career and current family life (as you can have kids later). That's their choice, there's nothing to be saddened about.
The 20s to early 30s is the healthiest time to have a child, for both the child and the mother. Now, you can have children in your late thirties and beyond, but that can get more difficult depending on the specific health situation of the parents.
Also, there is a problem in parity for how having a child affects men vs women. It is easier for a man to become a parent and maintain a career than it is for the mother.
I don't think it's much of a problem, let alone a solvable one.
Some women manage to have top careers while bearing children. It's just that most prefer to focus on their family. I'm female, in a field which recently swapped from male to female dominance. The market is flooded with part time jobs (saturdays, or wednesday when school's off) and it's definitely causing some recruitment problems in the field (and on a deeper level, female are less likely to become partners because of responsibilities and work involved, many stay salaried and thus have lower revenues, etc). There has been numerous studies on this topic in my field and family is the biggest factor holding people back (although men also value their off time more than they used to so its partly a generational thing). At least there's work for motivated people, so I don't complain.
To me it's rather obvious that most women don't value their careers that much. Which is not a problem in itself, just stop pretending otherwise, no one's holding anyone back from careers but people themselves. (I guess most men don't either actually, but it doesn't show as much.) I also really don't get why it is such a punishable offense to assume in recruitment that a childless woman in her thirties will be on maternity leave soon as it's indeed a really strong probability. It's not like waiting for the end of probatory periodto get pregnant is a rare thing...
