What is something that only exists because people are stupid?

They can be good negotiating points, though. Often, they will reduce the price of the vehicle more than the cost of the add on because they make more profit on the add-on than the difference in price of the car. And often the add-ons are preinstalled, so they have to give them to you anyway. Not true for all brands or dealers, but works for some.

With my last car there was a windshield coating, leather seat coating and bumpers on the door edges. After getting them nearly at the price I wanted, I told them I'd buy the seat coating if they'd lower the price another thousand below my previous price. The windshield coating and bumpers were also on the car when I finally got it. But I didn't get the warranty on them, of course.