It’s not woman-exclusive and also the companies deciding the sizing are not the same as the companies running department stores (for large clothing brands these days, online shopping in their own store would be optimal, since retailers take a large cut).
It’s mainly that making sure sizes are actually the same costs more money than just going with whatever comes out, and it’s hard to make purchasing decisions based on size consistency once a large amount of brands do this.
3.6/2+0.36 = 2.16
(10% of 36 halved, so 5%, plus 1% of 36)