The most obvious reason is SE's gender dynamics. The vast majority of new Q&A site participants come from other SE sites, which are based in programmer culture and other interests associated with masculinity. (See list of sites by age and this analysis of a 2015 SO developer survey, which does a better job at revealing the overtones of the survey, namely what is attributed to the field's demographics rather than lack of affirmative action.)

  The usernames associated with our current proposal skew towards male-sounding names, so the site is seeded either with male questions about feminism or male perspectives on what is important/interesting about feminism. These are all handicaps preceding the actual site content and whether the rule- and rep-driven Q&A format even appeals to the type of users who would visit and contribute to such a site (compared to discussion formats or communities that drive a softer line on detached objectivity). Other SE Q&A sites associated with feminized topics should be expected to perform similarly, as I believe they currently do.

If I can permit a personal aside, this is one of the main faults of techie libertarianism: a coalition of the willing/interested means that participants will skew towards those naturally predisposed to the format/task with ample free time. How does that demographic overlap with the one we would want for this site?

As for what could be done, I think first would be acknowledging the above (at least in the broad strokes), possibly with some acceptance of how this would currently be a male-driven site about gender and feminism. Second would be outreach to existing communities of feminists and gender-discussion communities, done with an attitude of seeking to learn rather than to recruit. Do these communities even have any need for a Q&A site? What do they think about the format, or what gives them pause? How would such a site benefit their hopes for the Internet? Are they interested in creating evergreen content about gender and feminism? It's simple in concept but difficult work that does not necessarily fall on any individual, hence why it does not happen—you know, much easier to just have a Q&A about it.

The most obvious reason is SE's gender dynamics. The vast majority of new Q&A site participants come from other SE sites, which are based in programmer culture and other interests associated with masculinity (see list of sites by age). The usernames associated with our current proposal skew towards male-sounding names, and the seeded content reads like male questions about feminism, or male perspectives on what is important/interesting about feminism. Other SE Q&A sites associated with feminized topics should be expected to perform similarly, as I believe they currently do.

As for what can be done, I'd start with acknowledging the culture of SE and why women might not want to participate. (Is rep-driven Q&A the best venue for attracting experts on feminism? But the most obvious solution is to ask actual experts whether they would be interested and why, and to use those results to fix the format. Simple in theory, but outreach is hard.