A big part of the problem with parts availability is the massive variety of parts needed for today's vehicles. The manufacturers don't make stuff the same for years and years like they used to. Now many things are changed every model year. Or even more often. Plus, there are many more manufacturers than there used to be. I don't know how they could possibly keep it all.
Y'know, that's part of it.... the move
away from standardized parts. There used to be 3 styles of headlight. Now there's 30,000. Mufflers used to be universal fit, today, they're specific to each vehicle.
It used to be one power window motor fit all four manufacturers. Now they change from car to car. The car companies would benefit from standardized/interchangeable parts by lowering costs, and the parts places could breathe a sigh of relief for not having to carry 29,000,000,000 parts for 3 cars.
