Typical Ohio. First sign of disagreement and you go running to tattle to Andrew Jackson.

In seriousness though, I went to refresh my memory about the cause, and it's just preposterous.
Congress divided the Great lakes area based on a terrible, but best available, map. A state boundary was supposed to run from the southern tip of lake Michigan eastwards until it hit either Canada or the north shore of lake Erie, and then come out the other side of lake Erie and continue until Pennsylvania. At the time they thought lake Michigan only went about as far south as Detroit, give or take.
When Ohio became a state they had started to hear rumors that lake Michigan wasn't shaped the way they thought, so they included some clauses in their constitution to ensure they had more northern territory regardless. Congress said whatever, referred the change to committee, neither rejected nor accepted it and then granted statehood.
When they incorporated the Michigan territory, they used their original definition because they hadn't looked at Ohio's proposed changes at all.
When Michigan moved towards statehood we had come to a clear understanding of the shape of lake Michigan, and so Michigan assumed they got the land that Congress said they got: southern tip of lake Michigan east until lake Erie or Canada. Which would end up being Michigan stretching from roughly Gary Indiana to Sandusky Ohio.

World's most tiny drunken border conflict later and the feds say Ohio wins because a state takes precedence over a territory, but Michigan was right on the cusp of statehood and they didn't want a fresh state to immediately hate their party so they traded it for a disconnected and totally disproportionate chunk of Wisconsin, which wasn't applying for statehood yet and hence didn't matter politically. Michigan was irate until it turned out the UP was full of resources that had more value than the shipping that went through Toledo.

(I can't read a wiki and then not share if I read it because of a comment. I have no regrets for the wall of text)