Why would thousands of entrepreneurs open GM, Ford, and Chrysler dealerships when the manufacturers could just open a store and undercut them? These laws were a promise to protect that business model.
That doesn't mean that such laws are a great fit for our current economy, but it started out innocent enough.
Yes, you're actually right - thinking about it, the issue is that these laws a) don't have any place in this day and age and b) were really abused in the case of Tesla, which never used the traditional dealership model to sell cars as far as I understand it (european here).
On a sidenote: One could argue whether these laws made any sense, even back then - just image how ridiculous it would be if every industry enjoyed the same "protections".
Originally the dealership model allowed car companies to rapidly expand their market without the costs of the infrastructure to sell to consumers, when they had enough money to do so they could easily strangle these businesses.
