You're right. There's a significant number of the population that will only buy American. The numbers are declining, but are still there. Saturns and Saabs are not American enough to appeal to this group. They're also not European enough to appeal to those drivers who want something European (typically meaning BMW or VAG stuff as Mercedes seems to have always been its own appeal). Then there's the growing numbers who buy Japanese because "it works."
The same thing sort of happened in the UK; when the population realised that most of the home-built cars really were not put together properly and really did apart after four years but the European / Japanese stuff was still working, trends changed. Many Rovers were considered to be good cars in their day, usually had design faults or characteristics, but weren't so "meh" to drive as something Japanese nor as expensive as something European.
Ahhh I remember the import restrictions on Japanese cars in the early
1980s...