This doesn't happen with other franchises like McDonnalds or Subway or 7-11. These franchise owners are not allowed to load up snake oil on customers, they deeply care about brand experience and all goods+services are tightly controlled in exchange for monopoly over some territory. Many of these franchises don't even have huge margins or profits. Car manufacturers somehow aren't able to do this.

McDonalds is a real estate company that happens to also sell an occasional hamburger. The FDA requires that hamburgers not be cooked in snake oil.

McDonald's corporate makes a lot of money on real estate. But every franchise is making it purely on those "occasional" burgers. It is that revenue that pays for the real estate.

Car manufacturers aren't able to do it because the car dealership lobby is a powerful one in state governments.