Women make up for around half of the mathematicians, and a solid percentage of economists, biologists and chemists are women.
Why do women avoid CS and engineering programs? I don't know, but it is the wrong question:
Why does it matter?
Faux diversity like gender and race is not something to aspire to. Finding students who have the aptitude and interest is far more important than meaningless demographics.
In my undergrad and graduate experience and working in industry women tend to fall along the same curve as men.
Very few are great, most are average and some suck.
The great female programmers bring nothing different to the table that the great male programmers bring. The female CS students that were great were naturally interested in the field and were self-driven into it. I have yet to meet anyone who was talked into majoring in CS that wasn't an abysmal failure.
So what does it matter if fewer women are interested?
I am far more concerned about universities dropping weed-out courses than faux-problems like attracting more women. CS and Engineering programs need to stop graduating substandard students, and instead these students should be booted out of the major and forced into brain-dead nonsense like business and communication.
It wasn't that long ago that the undergrad program I went through had 4 weed out courses(2 were CS courses and 2 were math), you had to complete it with a B- or better to pass, and you only had 2 chances at it. There was also a weed out written and programming exam that needed to be passed to get promoted to a upperclassmen and take 300 or 400 level courses. All of that is now gone.
Every course in my graduate program started with a qualifying exam, which you had to take the first or second day of class and you got dropped from the class if you failed it which meant you might as well drop out because it was a small program and each course was offered once a year. It was a masters program and not a PhD. program but less than half who started made it to the point where they could start their thesis or project and less than half of those made it to and passed the defense.
This isn't a "I had to walk 10 miles in the snow both ways" whine, this is a specific reason why CS graduates suck today and why it doesn't matter what the demographics of CS majors is.
That is the sort of thing that needs to come back, not a senseless drive to try and force women into careers they aren't interested in.