It’s partly because they think that other brands are better, partly because of brand loyalty. In my family, we always bought American cars, partly because we wanted to support American firms over those in other countries. Many people buy American because their parents, grandparents, or other family members did. Only a small fraction of customers make purchasing decisions based on true comparisons.
Buying a car is a big and expensive investment that is made only every few years, if at all. As a result, if you make a poor automobile choice, you’ll be stuck with the consequences (which might be rather pricey) for years, so you’re reluctant to return to a brand that has failed you.
With the exception of Tesla, which is an anomaly since it was developed on a niche market that has thrived in the industry, no American vehicle has ever been acknowledged internationally as a model of high quality or performance. Tesla is moving its production out of the country, making it no longer a “Made in America” company.
Automobiles in the United States have improved significantly from the horrible old days of the 1970s and 1980s, when they were poorly built. In the 1980s, when foreign (European and Japanese) vehicles made such major inroads into meeting American customer demands, American automakers HAD to compete. Ford, which had the poorest reputation, countered with a “Quality is Job One” campaign.
The new models, which debuted around 2016, are vast improvements over previous models, and I’ve seen quite a few nice-looking American cars while traveling abroad, but older models, such as Jeep, were notoriously unreliable and difficult to find spare parts for, depending on where you live in the country.