It is a pervasive cultural challenge, and it begins with regulation of advertising, which increasingly stereotypes women as being more concerned about keeping their nails intact than thinking about driving heavy equipment. There is that. It is well established in educational research through detailed gender-based analysis that this kind of streaming of women and men begins as soon as they set foot into any kind of culturally organized institutions.
By the time women reach university career ages, the institutional factors are already very discouraging. Walk into an engineering department at Queen's in the fall and you'll see people painted in purple from top to bottom, kicking jackets for miles at a time down the road as part of their initiation process. It just doesn't appeal to female culture. Even with a female dean of engineering in Queen's, it's been really difficult to get past that cultural barrier that is constructed and maintained.