MTF are just easier to spot. Due to the way gender is, and the imbalance of clothing, it's more evident for a physical male to cross the gender boundary than it is for a physical female. If you seek to wear a dress, or whatever, you're breaking a rule. Due to the fact that, in our society, it's seen as bad to be feminine (especially if you're giving the keys to the masculine role).
I know a ton of females who only wear mens clothes. Do they identify as male? Some do and some just don't care. They can blend in a lot easier. It's quite evident in a lot of fandoms online.