People have now decided that American cars are junk, even though that really isn't true. With a few exceptions, most of the highest mileage cars I see out there these days are... American. Things you wouldn't expect to see with high miles like a Chevy Cavalier or Ford Focus. Crown Victorias and Town Cars with hundreds of thousands of miles.
All that said, what's coming out of those doors is just fine quality wise in general.
GM, in particular, is using the same parts bin they have for decades.
Why does every GM four cylinder still have the low-speed, high-torque, starter that sound like it's on its last legs when it's brand new *and which is very intolerant of a low battery)?
Why does 80% of their line use the same crap window switches they have 15 years, and which tend to break? Why do their general-duty power steering pumps still tend to squeal like they have for 25 years?
When was the last time GM introduced a totally new engine that was not a V8?
With GM, particularly, all their engineering money and priority has been in the top of the line.
If you pay for it, you can get new design reliable components. But their general-duty stuff is junk, and that's what turns people off and prevents them from buying GM stuff down the line.
And, why do you see Cavaliers with 200,000 miles on them? Because you can buy them next to nothing and fix them cheap, because every shadetree mechanic knows downmarket GM products. They may still be on the road, but they tend to be rolling piles with next to nothing working properly (including the engine, transmission, steering, electricals, and brakes).
Meanwhile a Honda or Toyota downmarket car will likely be running pretty well at 200,000 miles.