Why are we still not seeing more house-husbands?

I grew up in what you might consider a fairly traditional family. My father worked, my mother stayed at home with me and my sister.

She cooked our meals, she drove us to school, she helped us with our homework. That was the sort of family that I saw not only in my house, but in the houses of most of my friends, and in the households that were depicted on TV and on radio ads.