Why does Michigan have such a heavy automotive influence?

I know I may sound kind of stupid asking this but it's been bugging me for awhile. GM, Ford, and Chrysler all have their headquarters in Michigan and mainly produce and manufacture cars their so I d just like to know why.

Detroit in those days was a major industrial center, partly because it was on the Great Lakes waterway, meaning shipping to Chicago or New York State was relatively simple. Both David Dunbar Buick and Henry Ford were in Detroit proper; Ransom E. Olds, founder of Oldsmobile, was in Lansing but moved to Detroit, presumably to be closer to suppliers. John and Horace Dodge were early investors in Ford; Henry Leland took over an early failed Ford venture and renamed it Cadillac. There were several dozen automakers in and around Detroit in the early days; major exceptions included Nash, based in Kenosha, Wisconsin, and Studebaker, in South Bend, Indiana. (Note: still near the Great Lakes.)

The main component of cars is steel and iron. Logistically auto plants were constructed close to the massive iron ore deposit mines of Michigan. Detroit and it's union became too self important and expensive for manufacturers to not bail on them.