Actually, Jenny, the number of spec script deals by women is on average with the historical figures going back to the 1990s, averaging between 13–14%. Last year the numbers were 13 female writers among 85 total which is 15.3%, slightly hire than average.
There are a lot of theories about this. One prevailing theory — although there’s no official way to support the numbers — is that fewer women write spec scripts than men. This is anecdotal based on conversations with script readers, agents, managers, and development executives. We do know that in 2014 (the latest figure I have available right at hand), only 28.6% of entrants into the Nicholl Fellowships in Screenwriting competition were female.
Interesting to note that 4 of 6 Nicholl winners in 2016 were women. 4 of 7 of the 2016 Black List Feature Writer Lab participants were women. Trend? Aberration? There’s just no way to know for certain.