It is a matter of fairness. If women are put off philosophy, and do not on the whole flourish in the profession, then it is unfair if they are able and interested and unsuccessful. The same goes for education as a whole. There is no reason why we should expect the various disciplines to be equally shared despite gender, class, ethnicity and so on, since in the past this has not been the case. Yet if some people are unable to reach their potential solely because of cultural influences stemming from the past, then this is clearly morally questionable.
Read another response by Oliver Leaman
Why is it important to have more women students and professors in philosophy? So long as there is equality in opportunity why does equality of outcome matter? Asians are even less represented in philosophy departments and Eastern Philosophy is given much less attention than the Feminist School of Resentment yet that isn't being challenged.