The answer may be gender bias in what gets published. Huffington Post did an interesting review of sex bias in publishing in March of this year; you should read it. Two months ago Scientific American looked at the same question with regard to hiring and publishing in the scientific community. They too found clear indications of gender bias, with, for example, the exact same materials being far more likely to be rated highly when a male name was attached than a female name. You should read it.