Discrimination on the part of gatekeepers isn't the only thing that can keep minorities out. A culture that tells them not to try doing it because it isn't their assigned role, a fear of being the only one of their group among a majority of another group, and earlier discrimination that prevents them from getting qualifications but isn't the fault of the gatekeeper could all be responsible. Given the information I know and what has been brought up in this discussion, University mathematicians could have been perfectly willing to hire women.