Some women think for themselves in the way they choose to obey more than to not. Some women, as do some men, find it far more productive to have a keeper at home to take care of all the needs of the home and it's environment than to *just not*.
Obviously, it is more about what each clan, sect, group, family finds best suiting and fitting for 'themselves' as a unit than any kind of defined and set agenda for masses in general.
There are definitely some days when it would be nice to have a "sister wife" at home, so I could come home and relax after work.
Women in polyamorous relationships do have that.