If your old enough to remember the John Cooper years, the Buckeyes every year would over prepare for the Wolverines mentally and physically, so much so that when they played the Wolverines they struggled to execute because so much was on the line. One wrong play, one bad snap, one bad throw, one bad penalty, one missed assignment could change the game and give the Buckeyes another 12 months of hell.
You ask why would Ohio State's DC leave for Penn State? Yes, the money increased. But I have a theory, that losing to Michigan and the fans reaction (even after winning the Peach Bowl Championship) caused him to look for other jobs.