"Why were American cars so crappy in the Seventies"
1. We still were in the era of people wanting a new car every 2 years, and thinking that 80,000 miles was a long lifespan for a car.
2. Emissions standards as well as crash standards were new, meaning that Detroit (and the rest, for that matter) were struggling to find solutions to those problems. Anyone else remember the Mopar big blocks of rubber that appeared in '73 for "crash protection"?
3. The 55 mph speed limit. This is the big one. Detroit stopped making cars for "turnpike" speeds and made them for 55 mph. The foriegn stuff was still built for higher speeds, and the difference was dramatic.
4. Oil shortages in '73 and '78. Detroit, then as now, makes a ton of money selling gas guzzlers that people really want. However, when the price of gas goes nuts, we all run to the small fuel-efficient stuff that people buy in places with permanant high fuel prices. Detroit built some great stuff in the late 1970's, but most people didn't want a V-8 RWD car (I had a few of those and they were bulletproof!).
Not only that, but they started putting 4-cylinder engines in their small chassis (which were already POS's) and even their mid-sized ones.
Of course, Detroit never figured out how to make a 4-cyl that wasn't a POS, especially when trying to power a midsize around. (I should add that Detroit's European subs understood 4-cyls a little better.)