I'm just speculating, but network effects are extremely important in science and I see it as very possible that women might have a harder time networking (presenting their papers, talking to peers, given benefit of the doubt by peers, etc.) in a field that is dominated by men. My SO did her bachelors on AA in big corps and found a lot of studies that supported the hypothesis that males bosses statistically tend to promote and acknowledge the work of other males more than of their peers. (Though I have to concede that it was just a bachelors degree and could also have been badly/unbalanced researched and that I am too lazy to find citations, as I have no clue of where she got them.)