I've always wondered exactly how that happens. MRS degrees (or the male equivalent) excluded, how do people end up as the stay at home person? Everybody in my extended family shy of 60+ years old works, so I can't really relate. I've recently noticed that a lot of my co-workers (mostly engineers) have stay at home wives (only one female engineer here, her husband works). I've got them figured out here as well though: all of these guys are financially set to retire, but just can't sit still that long, whereas their wives are of calmer personalities, worked their 30-40 years, and are happily retired. Several of these guys have "failed at trying to be retired" at least once.
I'm referring more to the 20-50 year old people of either gender who are unemployed by choice, and not because they are caring for others (kids/elderly relatives).
I can't imagine that many people grow up thinking "I'm going to marry a him/her and stay at home cleaning our house and cooking food all day", but it seems to happen that way.
Thinking about it more, most of the people I know (but not well enough to ask about this) in that situation have a spouse that has a huge income (a couple doctors, a CEO, etc). On the other hand, they weren't always that way. Do you just sit down one day and say "It isn't worth the income, I'm just going to stay at home from now on"?
Edit: I'm going to be out for a couple hours, so to throw this in up front, I'm not trying to be insulting to anyone, I'm just curious.