This is one of the first questions I ask when buying a car. Do you put that stupid badge on everything you sell? I make it clear no sale if they do. I bought the car, you made your money, I'm not advertising for you, end of transaction.
I also think it is in poor taste to have prominent logos or brands on a product… if the manufacturer is going to use me for advertising that needs to be explicitly the deal: they provide the product free, and then we can negotiate how much they will pay on top of that.
As another said, this is due to lobbying, but that doesn't change the fact that the markets are different.
Most individuals selling a used car, especially wealthier ones, aren't too interested in getting the most money from it, but just want it gone to move on with their lives. Not so with dealers, if they can't get you to pay a huge margin over what they bought it for (a price you could also buy one for) they'll wait for another buyer.
I'm not fundamentally opposed to buying used cars from a dealer, but when I've researched fair market prices, I've usually not been able to talk them down to anywhere close to them... whereas I've had many times where private sellers took an incredibly low ball offer I wasn't really expecting them to take.
Also, you've totally missed the point. They own the car. A person riding the bus does not own the bus nor get a say in how the bus is decorated