I recently came across the tongue-in-cheek conspiracy theory that consumerism has reached its endstate in that companies now intentionally design only good-enough-but-unsatisfying products because those make you more likely to continue shop around for something different-but-equally-unsatisfying, so just like planned obsolescence but more based on dissatisfaction.

I think there is some truth to this in that it's likely profitable to flood the market with mediocre products (especially if you do it through a white label network of "competing" brands) as long as you can avoid refunds (and on Amazon certain sellers make returns intentionally difficult by providing Chinese addresses without a prepaid label, making you pay more for the return shipping than you likely paid for the product to begin with). This also drives down the overall expectation of quality and reduces market pressures for quality while also completely swamping any competitor trying to sell a genuinely high quality product by making reviews completely unreliable.

I don't think this is a coordinated strategy as with whitelabel dropshipping being sold as a get-rich-quick-scheme for years there's no real need for it. Plus as you mention in many cases this is simply a consequence of a race to the bottom earlier in the supply chain resulting in nearly identical mediocre products even when some parts differ.

Personally I've run into this when picking out interior doors for our new house: despite being in the mid-tier price range, various aspects ranging from the veneer to the locks are extremely underwhelming but apparently on par with other doors in that price range. There's literally no reason the locks should feel like cheap plastic toys but it's something that's not visible and can't usually be tested even in a show room so apparently that's where they decide to cut corners. And because even standard sizes are considered custom, there's no way to return them, let alone once installed.