There are probably selection factors at play too in that there are simply less men available who want to be househusbands than there are women who want to be housewives.

Successful men are probably also sexually more attractive to women than vice versa, an aspiring househusband with a low paid job would probably find it harder to get a date with a female CEO than the other way around.

http://www.anthro.utah.edu/PDFs/ec_evolanth.pdf