The "rich" mapped to our world are the middle class (which only barely exists in Ankh-Morpork, just like it only barely existed historically in the real world). We could define "middle class" as the people who can afford to buy boots that last, but can’t afford to buy boots that don’t have to last. Exactly the bottom of the U curve I mentioned.

This is why wear-once ultra-fast fashion is attractive in the first place: not only is it cheap (in a very short-sighted sense) but it allows the less-than-affluent to signal affluence (by never wearing the same outfit twice – we call this "being fashionable" but of course being fashionable has historically been about signaling wealth first and foremost).