I have seen hot chicks request G+ invites on FB, so perhaps this speaks to your friend circle on FB. :P But you do have a point; the ratio of females on G+ is so far low and the few that have it are "unpopular" as the most popular users being mostly guys: http://socialstatistics.com/?number=100&kind=user-circle...

I doubt that G+ will fail for this reason, but with more well-balanced demographic it could probably get critical mass faster...