When that first baby is born, and even before that, while the wife is expecting that baby, any number of things might happen that would make it difficult for the wife to keep on working. I had to stop working in my sixth month (my husband was working, too), when someone pushed my as I was going up the stairs from the subway. The baby and I were both fortunate not to be injured seriously, but I was NEVER doing that commute again and risking another fall. There are women who are sick throughout their pregnancy, and at the very least they are extremely tired. It is an unfair burden to put on a woman to expect her to do everything, be pregnant, work outside the home, do the cooking and cleaning at home (because if there is only ONE income, cleaning help is not so affordable these days),and still also manage to have time for her husband.
Yes, some women ARE able to manage to do it all. But personally, I believe that is mostly hype from a generation of women who were raised to believe that being a homemaker and mother is for women who were not smart enough or talented enough to do something more important with their lives. If that were not true, then no one would be asking shadchanim, “And what does the MOTHER of the boy/girl do?” it would be irrelevant.
Regarding R’ Aisenstark’s statement about children being home until age five (an idea which I used to personally believe myself 30 years ago) – that only works nowadays if a) there is a parent who will consistently primarily be home with that child, b) that parent who is home is actually putting real effort and kochos into rearing the child, to keep him more or less on par with other kids his age, and c) the child has friends who are also home, so he can be socialized with them. It is VERY difficult to raise a healthy child in an environment completely devoid of interaction with other children in his peer group. So if all children in his neighborhood are in pre-school, he probably needs to be, too.