While some of the gender disparities in academic fields might be due to interest that isn’t the whole story. Importantly, it does not account for the fact that women are under-represented as compared to their percentage as undergraduates.
Rather than resort to sexism as the explanation, the reason may be more benign. Women’s partners are, on average, less willing to move. A high-achieving male is more likely to have a lower-achieving female partner, while a high-achieving female is more likely to have a high-achieving male partner. High-achieving people generally are not as prepared to move to another state because their job is not so easily replaceable.