Downplayed: Although Bob does most of the housework, Alice also helps out a few times a week.
Alice likes her job, but she and Bob feel that someone should be home with the kids.
Bob likes domestic stuff.
Bob works from home or telecommutes; Alice goes to the office. Since he is home, it only makes sense that he take care of the housework in addition to whatever it is he does in the home office.
Alice sucks at cooking and housekeeping, but somebody needs to do it. That somebody ends up being Bob, and he is good at it.
Bob is a single father.
Alice earns enough that Bob doesn't need to work, and any income he earns would be just excess. So Bob decides to do housework and look after their children for something which both feel is needed much more.
Alice and Bob decide that with the high cost of raising a child to adulthood, it's better if the household has both their incomes. The kids can be sent to daycare, or a nanny can watch them while Alice and Bob work.
Alice and Bob have a nanny to watch the kids, a maid to take care of housework, and a gardener to take care of the landscaping. Alice and Bob may or may not be employed, but the point is, domestic work is of little to no concern to either of them.
Deconstructed: Bob doesn't have the support of mainstream society.
Reconstructed: Bob manages to network with other stay-at-home dads, and has someone to lean on.