So, he has had a more than 30-year career coaching at a high level. I don't know how old he is, but he is certainly old enough to contemplate retirement. Those are the reasons why this seems normal.
But some things seem to be pointing towards that he didn't decide this on his own. Why leave now when we are likely to have our first full season after 3 suspended or canceled seasons? It doesn't make competitive sense that he was forced out, as in the last season completed (2019 XC) his women's team won the Big Ten meet. He currently has the best distance runner he or MSU may have ever had in Morgan Beadlescomb (13:31 outdoor).
I am also surprised that he stepped down, and they do not have a successor lined up.
It is rare at a top school that a coach just retires, they are usually replaced by somebody and forced out, or they plan their retirement like Harry Groves.
Does anybody have any solid and non-speculative insight into this?