Why there are not many women in the CAD design?
Wait for it. The idea that women couldn't or shouldn't do certain professions was around for a long time. Several decades ago this opinion started to shift, but I don't think there are many parents pushing their daughters, or encouraging them, to seek careers in engineering. I think you'll see a lot more in this field, in the next few decades.
Maybe a stereotype, but women are generally not inclined to technical mumbo-jumbo stuff (look at all other stuff where woman do not appear to be the majority - hi-fi, computers, mechanic work related stuff). Unless it's related to their work of dreams. However, women who choose to do that sort of work, do that perfectly. Sure, they love to listen to music, know to work on computers, some even build racing cars, but they are (if I may say so without offending anyone) more inclined to art than mechanical engineering. Maybe something to do with hormones, millions of years of evolution of homo sapiens, you know, child birth, keeping the fire on, cooking, taking care of children while the man hunt, or nowadays sit with a bear can and watch some sport or news on TV... Not me, though :)
(only my humble opinion, don't take it against me)
There are not many women in CAD design because there are not many women taking engineering courses especially in Civil works for it needs expertise to be able to compete in the field of CAD Designing. I love Graphic Arts and creating something, making a solid works and viewing the success or the result of my designed and give me a challenge to study and learn, more, researching in the world of CAD designing.