It's because it is. The short version is because it's socially acceptable for a woman to be somewhat masculine but it's not socially acceptable for a man to be feminine. A man wearing makeup, a dress, etc. stands out way more than a woman wearing a suit, jeans, etc. It is believed that this results in higher rates of transwomen. Obviously this is an oversimplified explanation, but it's the gist of it.

Source: Multiple degrees in psychology.