Back in the last century, auto dealer franchise laws were adopted in response to the monopolistic behavior of car manufacturers. They also kept a portion of the profits from car sales in the states where the cars were being sold. The inefficient layer of middle-men may have inflated prices a bit but some of that money remained in-state where it could be taxed for effectively.
Now,Tesla is challenging that business practice. In any given location, there aren't enough cars sold to support a traditional dealership. And the prices are already steep enough such that bumping them up to support middle-men would hurt the small volume of sales even more. Furthermore, no smudge-pot car dealership is going to be effective at selling Tesla's because of the conflict of interest that comes with selling a product that would supplant the product line that generates almost all of your profits.