This is interesting:
An unusual angle to the question of why clothes must inform us about a person's gender. My take on that is somewhat different but I'm still too jet-lagged to launch on a longer writing project.
A short summary of my ideas would begin with the question why it is so important for clothes to tell whether someone is a man or a woman, and the answer to that immediately dumps us into the jungle of different gender roles, different esteem and value and a different place in the societal hierarchies.
That currently in the West boys and men are punished more than girls and women for wearing the traditional garb of the other sex probably can be explained by two things: Homophobia on the one hand and the lower value of all things female on the other hand. A girl dressing in traditional boys' clothing (a tomboy) is aiming upwards, a boy dressing in traditional girls' clothing (a sissy) is careening down a chasm.
The situation elsewhere is more complicated and that's where the longer post would be necessary. But I think most of the dress rules in the West have been relaxed and that makes some people's discomfort of men wearing dresses etcetera stand out more.
Then, of course, various religious men have always worn dresses and nobody has complained...