Perhaps its a combination of CS being predominantly male-oriented with all the trouble that brings for a woman trying to 'break in', and low-status as well.
High-status occupations are sought after and reach gender equity even when there's a high barrier to entry. Examples would be law, and medicine (doctors).
Secondly, no woman in the several most recent crop of graduates (from the US) I know has been trying to get into a call center job. The one I most hear is "I want to work in a non-profit job in DC / New York / <insert big city here>".
Thirdly, with the more or less egalitarian society for people under 30 in urban areas, social status is much more important than economic status. There isn't any society-wide mocking of people who work in call centers, but there is some of people who work in tech. Ergo, less people (and specially women) go into tech in their 20s.
Witness the many TV shows making fun of STEM-concentration people, The Big Bang Theory, The IT Crowd, etc. In any film, the hacker will typically be shown as the over-eager, quirky, physically weak character (think Charlie Day as the kaiju scientist in Pacific Rim). Unless the film is something edgy like the Matrix, people always expect to see computer professionals as low-status individuals.
In my opinion, this results in women being afraid to enter these fields, because they are painted as having low social worth even if they have high economic worth. (BTW, if you live in Silicon Valley and are used to coffee-shop discussions about your favourite JS libraries, remember that it is a distorted reality field; if you are male and work in tech elsewhere in the States, the most people will come up with is "Do you work in IT? Oh, I see...")
On the contrary, in the former Soviet Union, scientists and technologist had a high social worth. Boom, 58% of engineers were women, as the article says.