BGSU also went on a long, slow slide after Meyer left and before Clawson got there. And they were awful after Babers left.
Kent State couldn't sustain the one good year they had with Darrell Hazell. Central Michigan fell off when Brian Kelly left, Butch Jones brought them back, then they fell off again. Northern Illinois sustained success between Kill and Doeren, but have been slipping under Carey. Stan Parrish couldn't sustain Brady Hoke's success at Ball State. Same with Jeff Quinn, who followed Turner Gill at Buffalo.
Yes, there are outliers (Toledo), but the point is that success is hard to sustain, especially in the MAC. And the benchmark Fleck set is almost impossible for any coach to meet.