Am thinking some of the cheaper thinner quality and shoddier mfg. materials started because of unrealistic government expectations and interventions of and for better fuel economy and emission standards into vehicle manufacturing before manufacturers were ready to implement them.
Then in order to increase economy, manufacturers reduced weight in almost any way they could to conserve fuel and partially reduce emissions. Then, after that, somewhere along the line, planned obsolescence, where purposeful lower quality likely took over? For example: Looked at a brand new GMC truck, the driveshaft was already rusty and it hadn't even left the dealerships lot. Not a lick of OEM paint on the driveshaft.