Paradoxically, back when the market was LESS efficient, the extra slack afforded higher standards because they could overengineer something and still sell it easily.
It always comes down to supply and demand. Supply of generic products like compressors and blenders skyrocketed. Increase the supply enough and you get a race to the bottom. All market inefficiency has been squeezed out of the market. The market has arrived at an equilibrium of making some things just high enough quality that they last longer than a few months while being as cheap as possible. Anyone trying to make something higher quality gets squeezed out. Unless there's also much higher demand to compensate for it.
There is enormous survivorship bias with this 'stuff was way better back in the day' argument - there have always been awful products produced, but those get replaced quickly. An awful fridge from the 1950s was replaced by the 1960s. Engineers weren't deliberately overengineering things back then out of some sense of pride, they were just worse at engineering (and material science) - some things were over-engineered, because we didn't know better ways to solve that problem, and some things were under-engineered for the same reason. I think the increased cost of labor relative to manufactured goods is a big driver of this perceived change, as nobody wants to pay a repair guy $500 to come out and fix their $500 fridge. If the fridge cost $20k we would probably still fix them and they would have a long lifetime (and the repair guy would still charge $500, like an HVAC guy), but there is almost no market for a $20k fridge when a $500 fridge is available.
The market only trends to maximum efficiency if information is sufficiently cheap for enough participants.
Most people have no cost-effective way to find out how long an appliance will last, so the market cannot find the most efficient lifetime for appliances.
It always comes down to supply and demand. Supply of generic products like compressors and blenders skyrocketed. Increase the supply enough and you get a race to the bottom. All market inefficiency has been squeezed out of the market. The market has arrived at an equilibrium of making some things just high enough quality that they last longer than a few months while being as cheap as possible. Anyone trying to make something higher quality gets squeezed out. Unless there's also much higher demand to compensate for it.