I think women are just less inclined to care about this kind of stuff. Maybe they are a lot more susceptible to group think and the desire to fit in, so they just kind of go with whatever people around them are doing. The phenomenon with the women going to church more I think is just more to stave off loneliness and socialize, and they are also more emotional so that aspect of a religion might resound more with them. Not as a serious theological argument, but just enough for them to go.
The more likely thing is that I think women are just a lot less likely to make "atheism" a part of their visible, meaningful identity. Since I don't think a lot of women really value this kind of conversation, a woman who is an atheist would simply never talk about it much.
The majority of women my age (millennials) I've spoken about this with were soft agnostics, basically not wanting to take a side, but certainly not living any specific religious tenets other than basic "killing is bad don't steal" shit.