Because men's and women's brains are wired differently. Guess what, i did not see many men doing knitting.
You would be surprised.
It is much more about society and upbringing of children than "brains being wired differently".
If you bring your kids up with your daughter being shown only "girly" or "appropriate for girls" stuff and your boy only "the boy stuff", no wonder. Ever been to a typical toy store? With aisles clearly delimited by color or boy/girl labels, with "boy side" having Legos, cars, guns (!) and "girl side" only dolls, princess outfits, make up and such? Also the peer pressure at later age when anything science/engineering is considered "nerdy" and "uncool" isn't helping.
A lot of girls are interested in technical pursuits but they tend to be put off - either by parents or later on by peers. I could see it clearly with my nephew a niece - while she is a typical "girly girl", she was pretty keen on things like computers, computer programming in Scratch, building stuff from Legos, helping my dad in the workshop, etc. But her parents aren't interested in that and aren't guiding her to explore it, more the exact opposite. So it is very unlikely she will wind up doing anything e.g. with electronics or engineering later in her life.
But it is "because men's and women's brains are wired differently". Yeah right.
