Probably because of school, I had to take geography class for 11 years and the states have definitely been a main topic for at least 1 - 2 years. And I'm living in Germany, we're famous for our cars and Detroit is famous for its automobile industry so we've probably also talked about it in politics and economy before :)
But the main reason for including it in JFTC was probably that my best friend was an exchange student in Michigan while I was writing the story :D