In my experience, it seems that the folks who get hired fit a desired “type”- for instance I worked in one place where it seemed like all the new people coming in were Asian women, or elsewhere, all the Marketing folks will be blondes, etc.
It seems (to me) that people like to hire people they think they will be comfortable with/around, and that overwhelmingly seems to mean that they look/act the same. On one level, I get this- that’s kind of how we “choose” our friends, right? You just seem to gravitate towards folks that have similar likes, etc. to you… but these are supposed to be workplaces… so I would hope that a manager/person in position to hire would appreciate the benefits of working with a diverse group. So far I have yet to see anyone in my places of work actively pursue achieving this sort of diversity.
I imagine that because ID has historically been a “boys’ club”, many of the folks in hiring/managerial positions TODAY are men. And because they like to hire what is familiar and comfortable and easy to them, the cycle just repeats itself, and female designers remain a rarity.