In the more generic case, states have these laws on the books to protect the local franchise dealers. These people buy cars from a particular manufacturer, usually multiple brands. In order to protect these dealers from the perceived threat that an automaker could come in and sell direct (thus undercutting their business), laws were enacted to require a franchise to sell vehicles. Thus Ford couldn't come in and sell vehicles unless they created their own franchise, which would raise their costs to be on par with the independent franchises. I think the justification for the protection is the local jobs and businesses.