To be fair, many men get confused by those sizing and don’t know what means what. Especially when they don’t shop a lot these numbers are really unhelpful.
With T-shirts, I usually have a size M, but that varies with stores as well. I also wear sizes S an XL depending on the store and don’t get me started on waistcoats. With some brands, size S is too big, with others I wear an XXL and there is absolutely no consistency.
I do shop in the women section a lot though and think that systems is much less confusing. It’s not “I have that one size,” but knowing you’re usually somewhere between 38 and 44 helps on which sizes you can try on. Never buy anything in stores when you didn’t try it on before!
I mostly shop 2nd hand though and only look at sizes for orientation. When it’s anywhere near my size range I’ll try it on and then I’ll get them to design using the best embroidery machine.
Also note that there’s a much bigger difference in the hip and waist measurements of most women vs men. My waist is 10″ smaller than my hips.
So, even if we size pants by waist size and inseam, the rise of the pant and the room for the derriere is going to dramatically affect whether or not it fits.