I thought it was pretty clear. Sexual Dimorphism doesn't operate the way you think it does. Women with high sex drives aren't rare at all.

I have heard that, for most men and most women, the time of highest sex drive happens at very different times (much younger for men than women). This might account for the entire difference, especially if your'e getting most of your information from the culture at large. As TVTropes will tell you, Most Writers Are Male.