Well we have true 4 seasons, the scenery is gorgeous. From mountains (Small I know) to white sand beaches we have it all. Snow in the winter for skiing, and snowmobiling. Hot sunny days for sitting on our plentiful beaches to enjoying the wilderness or many lakes and streams. Not to mention the history that dates back to 17th century when the french were settling and fighting the Indians. There is so much to offer beyond all of that. You have great food, gambling, and sports.
Well if you visit the St Clair and Detroit Rivers (between Port Huron and Detroit), you can check out the lakers and salties (big ships) that traverse these waterways carrying all kids of goods from grain, to iron ore and coal, to windmill towers & turbines.
Make it an international trip, cross the river to visit Canada!!! Just remember your passport.
Beautiful area but no hotels to speak of within an hour of the track. Plenty of camping and cabins nearby, reserve well ahead of time if you plan on attending a race.
No way I could narrow it down to just a single reason to visit Michigan. Water, Woods, Wines, the People; those are the top things I can think of, and about as short as I can make the list.