Do you think it's a natural market behavior that enticed manufacturers to aim at entry level market by cutting corners AMAP then realizing it also increased frequency of renewal thus making even more economical sense ?

Personally I believe this is the default behaviour of unrestricted market competition. Under competitive pressure, companies try to cut costs by gradually optimizing the product into the cheapest version that still sells - which in the end will be so tight on tolerances that it'll break quickly.

I suppose at some point there were business people who noticed that planned obsolescence creates repeat purchases, and that pricing is an arbitrary thing so they can sell the same hyper-optimized crap on different price tiers and people mostly won't notice - but I think the main driving force wasn't malice, just the usual thing that happens in the market economy.

In this way, I see the period of 1960s - 1990s as a time of discovering new ways to cheap out on materials and construction. After all, optimizing for manufacturing costs takes time and lots of smarts. Barely working crap doesn't happen by default (conversely, and this reminds me of the discussions around Juicero teardown, the initial design of any working appliance will likely be heavily overengineered).

yeah I know that cutting cost is almost a definition of business, I meant the fact that in the same time it forces a different rhythm that is very self sustaining; it's a double win, and I wonder how long they knew that fact. It's probably a naive question, I remember seeing old quotes about "if doctor cured you of all, they'd be jobless" or one about Michelin "they knew how to make 10x better 10x cheaper, but why should they release that".. it's just the dual.