You cant measure clothing in terms of Dollar Value. Or Revenue, and it is less would means people are buying less. That is I think so far from truth. People are buying more from Uniqlo or other much Cheaper brands that offer better value.
We all know the manufactured cost of any clothes is absolutely minimal. It is the design, marketing, and Retails Rental that covers vast majority of the expenses. It also enjoy very good economy of scale.
Material improvement means T-Shirt that are cheap today are likely to be much better then cheap T-Shirt 10 - 20 years ago. It comes to a point where these cheaper alternative are good enough.