What surprises me is that the OP apparently thinks that anybody proclaiming that they're female on the Internet is actually female
There are plenty of females. They're just not the same set as the set of people who say they are female. Sure there's some overlap, but you'll never know in any particular case.
As for the 12% or whatever it currently is on TESOCensus, I don't believe that's an accurate representation... has to be WAY more than that. Well documented that most (not all) internet forums have a strong male bias relative to the populations they represent, and I think that's reflected in the census numbers (since the only way anybody would find that site would be through a forum).