This may be true now, but it definitely wasn’t, once upon a time. In the 80s-90s there were hordes of young women in SF, and it seemed that all of them were looking for guys. The sex ratio was very skewed.
It wasn’t the sex ratio, it was that so many men in SF are gay the pool of available normal men is much smaller. SF is one of those cities where the BS claim of 10% of the population being gay is likely an understatement.