Women in the Economics Profession

It's no secret that women are underrepresented in the economics profession. Part of this, as has been pointed out by many, is a selection story: women aren't attracted to the economics profession the way men are. However, Christian Zimmerman, who runs the RepEc service, posted the following:

Women have always been underrepresented in Economics. For example, regarding US faculty, the Committee on the Status of Women in the Economics Profession (CSWEP), a subcommittee of the American Economic Association, determines in its latest annual report that women represent 28% of assistant professors, 21% of associate professors and 8% of full professors in PhD granting Economics department. As a whole, they represent 19% of all Economics faculty.

The point of this post is not to complain about the low proportion of women in the profession, or about their dwindling share up the ladder, but about the lack of involvement on women in RePEc. Currently, their share is at 14.5%. It is clearly below the 19% mentioned, although it is slowly increasing (it was 13.6% a year ago and 12.7% two years ago). Why this underrepresentation?