That was my initial though as well, but I came up with at least one case where survival of the dealerships is critical to an open market place.

If all stores were owned by car manufacturers, that would be a significant barrier to entry of new automakers. Not only do new entrants have to build a car company, but now they have to create a new distribution network as well at the same time.

That said, Tesla is a new car company and creating a new distribution network for them does not seem that big an issue.