My view is that Detroit’s quality issues were always due to cost cutting. And outsourcing was part of cost cutting. Just like it was for Boeing.
They don’t outsource for any other reason than cutting costs.
Japan captured a big fraction of the US market with vehicles that were significantly higher priced. They are still, but not as much as in the 1980’s and 1990’s.
Detroit cost cutting started in the early 1960’s. You can see it in the interiors of the cars year after year after 1960. But there is much more that is hidden.
A switch to cast cranks and powder metal rods. Shoddy castings full of flash, residual sand and core variations. Flimsy cheaper designs for almost everything.
Lousy body designs that created moisture traps (but cheaper to build). Thinner sheet metal that rusted thru faster. Shoddy primer and paint application, skipped body prep steps to save money, and a change to E-coat which initially made things worse.
Even when the added content to improve quality, they half assed it, and had problems. In Canada, the paint over zinc coated metal quickly peeled off because of inadequate (read cost cut) zinc surface prep.
Cheaper wiring harnesses than the Japanese. Cheaper electrical components, cheaper cooling and ac components... every component and assembly process on the car.
Many of us still drive Japanese cars due to that reason.
We know that quality control from Detroit is crap.