Better check on that stat, I think it is something like 30 years old.
I have no idea, I do know that neither NC or TN are not even in the running. TN is water impaired, a few shallow rivers, very few natural lakes and some man made ones. NC has little to offer on the fresh water side. A few man made lakes and shallow rivers. Few natural lakes. They do have salt water. IF any state took Michigan over it would likely be Florida. I am only speaking of recreational boats with state registrations. No commercial boats, or federally registered ones.
It is not that important to the question. The boats made in those states, for the most part, are sold else where. Why are there so many boat builders in TN? I contend it is a better tax and wage structure.