Urban is an executive in a very large organization. He also needs to understand that sometimes you cannot hold onto people, even if you think you can help them overcome whatever challenges they face, because the risk to return ratio is governed by forces outside your control. When that happens, you put not only yourself at risk, but the entire unit that you control.
I'm not saying that he did that, but to some extent, he will be carrying the responsibility for the decisions that he made. If you have been fortunate enough to have a mentor, and I have had some exceptional ones, then you will understand perhaps why he hung on to Zach Smith so long. I'm talking about someone who puts himself on the line for you, so that a special bond forms when you make that trust pay off.
She or he might get their return on taking the risk, but you still feel indebted as you age because you know what taking that risk meant in your life and how badly the risk that your mentor took on your behalf could have turned out if you didn't.
You also know that there is nothing you can do to pay the person back except to take risks for others in the same manner that your mentor(s) did for you.
Earle Bruce took risks for Urban Meyer because it was in both of their interests and Urban Meyer exceeded performance expectations. When you are in leadership, that is the best that you can hope for. Zach Smith, on the other hand, even if he did not act violently toward his wife, did not meet expectations. To me, it is that simple. Urban Meyer will learn from this. The error was not to take the chance. The error was to ignore that Zach Smith's behavior on the job proved that he was not Urban Meyer.