I don’t see the point in doing men’s vs women’s clothing sizes. Surely there’s a big enough variance in size and shape between individuals that it would be more useful to size based off of measurements of body shape?
Take shoes for example. Why is a uk men’s size 10 so wildly different from a UK women’s size 10?
All it seems to achieve is making shopping for clothes difficult for anyone that doesn’t fit into the expected body shape for their gender and make it hard to find well fitting clothes outside of specialist shops.
The zipper in th3 back also helps if you have a big chest and don’t want it bifurcated by a zipper.
And you can’t put that same zipper (if it goes all the way up the back) on the side… if you have wide hips.
So at least that still has reason to exist.
Source: my own body and never wearing a front-faced zipper after seeing why we don’t do that.