Most Helpful Guy
Another reason, besides the ones previously listed, is that women's clothing tends to be much tigher and form-fitting than guy's clothes, but women's bodies have more complicated and varied shapes, and lots more areas to measure and to fit right.
Guys buy pants, and it's all "waist and inseam", but girls not only also have an extra measurement (hips), but she also wants a certain fit in her ass, and may have to try several brands or lines to find ones with a fit she likes. Same with shirts; you have boobs that require more work to fit, especially with tighter clothes or dresses. For a guy, most stuff is one size measurement (M or XL or whatever), and even for a dress shirt, it is neck size and chest size, but no need to worry about detains beyond those.