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).