The cars in NASCAR are just billboards for advertising. It's racing in the sense that they go over the national speed limit, but NASCAR is just a business that sells advertising and has consession stands that sell food and drink. If you brought a race car to the track they would not let you run it. you don't have to win a race, as an entrant, to receive value for your advertising budget. They have made sure of that. We all understand that even though it might say Chevy on the hood, that there might not be any Chevy parts on the car. You might be able to change the name to Ford on the hood, change a few parts in the engine and now be racing a Ford. You don't build a better racing car by doing something new, you optimize the rules. If you do anything else, it's called cheating. Why would a manufacturer pull out? Not because of NASCAR, but maybe because of the manufacturer's own internal business decision. They know the rules and costs going, and success in an advertising campaign is not connected to winning. That is one of NASCAR's strong points. They have made mediocrity the gold standard in racing.