For one, a built-in social network. For women who didn't have very nurturing mothers, they can find surrogate "mothers" in the congregation. For co-dependents, there is a never ending supply of people who need to be "helped." Ambitious women can control a tremendous amount of the tone of the congregation with social gatherings, and influencing their husbands. Praise and rewards for being "traditional," it's very easy to get kudos for being a stay-at-home mom when you're a witness. "Headship" means never having to be responsible for bad decisions, since the "head of the house" is the primary (some say ONLY) decision maker of consequence in the family.
Yes, women give up lots of power to be JWs, but if you can get past the mind-bending, thought-numbing cultishness of it all, there are definite bonuses. Just ask my mother.
I'm not saying any of those things would be motivators for healthy, happy women, but they are getting something out of it.