With the present social standards in place, it is far easier for a genetic female to venture into the male world than vice-versa. Socially acceptable attire for the female even includes a menswear line. A womenswear line is unthinkable. For transwomen, it's all or nothing.
Due to the life changing realities of gender transition, it is easier to make a move across the gender line, but short of complete transition, than it is to announce to the world you are changing genders, undergo surgeries, do all the legal document changes and present as your identified gender. The option is there for transmen. It is not there for transwomen.
I realize there are the realities of surgeries and other factors but what I've stated above does have a substantial impact on the apparent difference in the numbers of transmen vs. transwomen.
Julie