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First of all, house work and child care are still time consuming as hell, and have to be done on a weekly basis. When you are already working long hours and taking work home on the weekends, it can be overwhelming. This is true even when you don't have kids.
Second, the division of labor affects people's careers. If you are in a competitive profession, then the hours you spend on housework are hours that you aren't spending on your paid work. Women (and men in two-career marriages) are competing against guys who don't have to spend time outside of work on other chores because they have wives doing it for them. And once things get too overwhelming for a two-career couple, guess who winds up quitting her job or scaling back her career? Yep -- it's the woman, often because she is doing all the household and child work anyway and is overwhelmed OR because it is automatically expected that she will be the one to make the career sacrifice. (After all, no one ever talks about "juggling" fatherhood and career, right?)
Third, these things are very difficult to negotiate in marriage. There is still very much an assumption that the woman is in charge of making sure the house runs smoothly and everyone's needs taken care of. Couples tend to automatically settle into that pattern, unless the woman makes a stink. But if she makes a stink about it then she is disrupting things and extracting "concessions" from her husband. And who wants to think of marriage as a power struggle? So a lot of women accept the status quo rather than make waves and take the consequences, while simmering with resentment all the while.