[bluGill]

Most people don't buy enough cars for repeat sales to matter. If you trade in your car for a new one every 3 years, and always go for the same brand it might matter. However if you sometimes buy GM, sometimes Toyota, then the dealer should assume that you won't be back because odds are you won't, and this is a common enough case that the dealer just assumes it for everyone. If there is reason for the dealer to believe you will be back to buy your next car you will get better service.

Worse for the dealer, everybody walks in having done their research. Most people know exactly how much the dealer paid for the car, and want it for that price leaving the dealer with nothing. There is thus no reason to treat the customer well when there isn't even any money to make. In fact the biggest dealers sell every car at a loss, making it up in factory incentives and post sales tactics which are bad for customer service, but what the customer really wants.

Most people don't buy enough cars to know what good sales actually would be. If you really want to know what good service is you need to average more than one car a month (sometimes it is every month, sometimes it is a large order every year). These customers are rare (always a business), but they do get a completely different experience as there is real reason to keep them happy.

For a dealer though sales are a distraction. They only sell cars at all because that is a cost of doing business to get the parts and service business. These are the real money maker. The first couple years they get everything (and the factory pays not the customer, always nice to tell someone there is no charge for major work). Many are trying to make themselves good places to go even after warranty is expired (that is reasonable prices).

The above applies to new cars only. Used car sales is completely different. (most new car dealers also make a ton of money on used car sales)