The reason Japanese cars are preferred over American cars is their quality and price. They are providing highly advanced cars with efficient fueling system in economical prices so that is why Japanese cars are preferred.
It is a catch 22 isn't it. Spend more on one thing than the other and the thing you spend the money on, has the funds to improve. The thing you do not spend money on does not have the funds to improve. Try buying American and start reversing the trend.
We cannot say that Japanese cars are way better than the American cars. It's just that some of the Japanese cars are built better than the American cars, and not all of it.