It originated as protection for franchisees. Early on, manufactures didn't have the resources to set up dealerships everywhere they wanted to sell cars. So they used the franchise model. The argument is/was, that the franchisees needed protection so they could be assured that their investment in a property, facilities, and developing a market in an area could not be taken away by a manufacturer moving in with a company-owned dealership.

Very similar to the complaints about Amazon moving in on sellers with their own products once they see what is selling well with independent sellers.