He is an idiot. There is no way to sugar-coat it.
He got his chance originally because he is French-speaking, was perceived to have paid his dues in the lower leagues and is a large man with a physical presence, which led to the perception that he is a motivator. He subsequently got a number of opportunities, including the Penguins and this one, because he had prior NHL experience, which compounds the initial mistake. However, there is no substitute for intelligence, and he will never be confused with a tactician. Nor will he ever be associated with anything resembling critical thinking.
While it's true that there are very few coaches that actually think the game, if we were to try to quantify their mental capacities and plot the values on an axis, MT would still end up on the pole coinciding with the most intellectually challenged.
That, to me is the number 1 reason that is at the root of any other shortcoming. At this point, MB is not looking stellar for having picked him.