What business in their right mind would want to sell or stock a product that comes with a label that says, in effect, “Don’t spend your money here, go somewhere else”?
So to be clear: if Apple printed on every iPhone box, "This phone is 30% cheaper on Apple.com", you feel that Amazon, Walmart, Best Buy, %LOCAL_TECH_STORE%, etc. should be legally obligated to stock those iPhones?
A better question is, why aren't iphones cheaper at apple stores?
So you think it's OK that Walmart doesn't want to sell a product that says, "Hey, don't buy this from Walmart", but you think it's wrong for Walmart not to want to sell a product that links to a website, where the website says, "Hey, don't buy any more of our stuff from Walmart"?
Nintendo will encourage you to buy from their online store, competing with Wal-Mart selling physical media (and maybe digital codes too on their own store?).
It's not in contention: it's both of those things. It's just that some people want it to be exclusively one of those things.