Amazon doesn't get free advertising. They lose out on revenue they could have gotten by placing another paying ad there instead. The opportunity cost is not 0.
Amazon chooses not to advertise third party products on those surfaces. They realize they have product synergy in giving away free films and movies to their customers, which is why they do it. It's a massively unfair platform advantage.
UPS and FedEx don't emblazon ads on their delivery trucks. Nobody is buying up those ad spaces.
