When Did Automobile "Sub-Dealers" Disappear?

As late as the 1950’s people living in smaller towns (far away from an auto dealer) could buy a new car through a local “sub” dealer. This was usually a local garage, that had a contract with a dealer in a larger town. The subdealer would buy the car and deliver it to the customer.
When did these things bite the dust? Was it because they offered a service that was not needed?