For example, we have a Vornado fan in my house that is probably from the early 2000s. It still works perfectly even though we've left it running 24/7 for weeks in humid or dusty environments (e.g. to help air dry a wet basement). In terms of money paid/hours used, we got an amazing deal on the purchase.
From the manufacturer's perspective, the life time value (LTV) of us as a customer was basically just one fan + the free marketing of folks like myself writing this kind of post. It reminds me of the joke "Did you hear about the company that made lightbulbs that lasted 30 years? They went out of business!"
It makes sense that manufacturers would start to lower quality at a slightly faster rate than they lower the price as this means that folks still feel happy with the purchase. Sure, the fan doesn't last as long due to what is essentially planned obsolescence but the company does get to stay in business.
Temu/Shein etc are just the logical endpoint of this line of reasoning. If you are going to wear a shirt for the one summer where it's in style, why would you spend a large amount of money on it? And in turn, why would the company selling it spend a lot of money making it?
(I should add, this is purely an economical argument and ignores the working conditions/health effects/etc)
Given there's zero barrier to substitution + the TAM for fans and lightbulbs is huge as sibling comment mentioned, there's no reason for the LTV to meaningfully exceed 1 puchase and the value of that free marketing could be higher than the EV of purchase N+1
E.g., if my name-brand turd wears out unreasonably, I don't replace it with the same name-brand turd; instead I replace it with an ephemeral Chinese brand turd which is just as likely to have similar build quality and features.
There’s probably an optimum for maximizing sales/growth that doesn’t land on highest quality products in the real world, with non rational consumers, imperfect information etc… sadly.