Spoil what? Mattel is definitely the biggest fish in the sea but they aren't the only one. Also, The purpose of the show isn't about any particular brand of cars or track. Realistically, adults are going to be interested in watching the program. Adults aren't Mattel's target audience for their basic cars.

I shouldn't be explaining Mattel's position on this matter. I wasn't involved and I don't know first-hand what is their reasoning.