I blame the stereotype they literally teach in latter school years in no small part---the one that says "all girls are better typists than guys, get used to it, but that's about all they have for it".
A Susan Jobs might have had that result, might not. The key thing is somebody on the young side coming forward and knocking something big out of the park----the deck is stacked enough against it as it is without over wrought age discrimination coming into play and making people think "I can't" needlessly.
The allure of (new) money would be pretty potent though, as what lists are generally kept are aimed at Wealthiest Men, with token women mentions almost always being Old Money, or business hacks ala Professional Wrestling/E-bay.