They futz with sizing because it's a part of their marketing. Fashion targeting older/ fatter people will have smaller sizing to flatter the customers.

I think buying clothes that don't fit just because you want to say it's a particular size is far more a part of female culture (in my social circles in the UK): womens' clothes are in "sizes", men's clothes are in measurements (inches/cms).

I don't think the industry, nor many of the customers for female fashion want accurate measurement-based sizing.