App Store is a distribution channel. And just like Best Buy wouldn't tolerate you bypassing their cut neither does Apple.
Can you clarify where they are not?
I feel there is a number that Netflix and others would be happy to pay to help onboard customers.
The difference is that Best Buy doesn't decide which appliances I can plug into my home outlet. I can buy a toaster from Walmart if I don't like Best Buy's setup, but I can't buy products from another store and put them on my iPhone.
That's not to say Apple is wrong, just that Best Buy isn't a good comparison to use. Apple is a distribution channel and a platform. Some better analogies would be Nintendo's requirement that any software running on the Switch go through their specific approval process, or maybe a printer requiring you to only buy official ink cartridges.