Cultural inertia. Men are domestic providers; women are domestic executives. Of course, those roles have vastly expanded for women; their options are now limitless. However, domestically, men are still limited to being providers.
Why? Because men don't have the collective impetus for change that women have had in the last half a century. We're passive partners in this society in many ways, simply beasts of burden here to pay the bills and do the heavy lifting. We accept our second-place role in the home because it is tradition.