I think it has a lot to do with how long it takes for changes in culture to become part of the mainstream consciousness. It wasn’t that long ago when gender norms were much more regid when all men were expected to play sports, be the breadwinner, and do “manly” things while women were in charge to housekeeping, being pretty, and taking care of the kids.
Although the definition of gender roles has greatly expanded, the perception of the traditional man and woman are still around and some of their effects can still be felt.
Although we say women can do anything men can do, we haven’t necessarily raised them that way. It is still the norm to expose boys to sports, power tools, and cars just as it is typical that women get exposed to cooking and playing with dolls.
I’m not saying that modern society explicitly defines what men and women can and/or can’t do but that women haven’t really been conditioned to consider all the possible careers available to them like men have.
Men are taught AND shown that they can be all sorts of things. You see it in TV, movies and other forms of media. I think you’d agree that female engineers, sports coaches, etc aren’t as heavily represented. If that’s the case then I can’t say I’m surprised by the smaller number of female designers in our industry.
I feel the solution starts with good parenting. As the first and last person your child sees in the day, you should create an environment that truly encourages kids to chase their interests, not predetermined societal norms.