Proximity to natural resources, skilled labor and growing market for transportation. At the beginning of the 20th Century, the industrial Midwest was at the center of the need for transporting agricultural goods (be it by wagon or train) from America's heartland to the major cities. The automotive industry naturally evolved from the convergence of those factors and grew upon the established infrastructure. (An infrastructure that Dubya's globalization policies undermine.)
So the government must do something to protect the jobs correct??
So he did.
He selected Detroit, and the rest was history.
Obviously, though, the I65/US31 corridor is better suited to supply the national needs than SE Michigan.
When market forces are allowed to work, they frequently do not arrive at the same solution an erratic, emotionally unstable individual such as Henry Ford or Joe Stalin might decide.