There is also the secular trend. Detroit's dominance in the auto industry wasn't an accident. Iron was mined in the Iron Range in Minnesota and shipped across the Great Lakes to Detroit. It was natural for manufacturing to occur there. Other GL cities had similar advantages, but e.g. Alabama wasn't a realistic competitor. Coal was also shipped, mostly from the Allegheny region, west across Lake Erie.
Today, less iron is refined domestically, and cars are made of more aluminum and less steel. Most coking-quality coal is now mined in the Powder River Basin in Wyoming. On top of that, the US shipbuilding industry has become less competitive globally, which together with the Jones Act has resulted in a significant drop in shipping on the Lakes. See Figure 2 on page 2:
Today, less iron is refined domestically, and cars are made of more aluminum and less steel. Most coking-quality coal is now mined in the Powder River Basin in Wyoming. On top of that, the US shipbuilding industry has become less competitive globally, which together with the Jones Act has resulted in a significant drop in shipping on the Lakes. See Figure 2 on page 2:
https://sgp.fas.org/crs/misc/R47550.pdf