What exactly do you think Apple is so inflexible about? Do you think they should make a different deal with Amazon that they are willing to make with Netflix, Hulu, HBO, CBS, DIRECTV NOW and all of the developers for the Apple TV Platform? Don't you think that would be more problems for Apple? Obviously neither of us are in the room so we can only speculate. But it just not make sense for them to have some other reason to simply tell Amazon they are not allowed on the platform when they are perfectly welcome on iOS with the same exact restrictions. I think it makes much more sense to speculate that Amazon simply does not like the restrictions that everyone else (not including Vudu) has found a way to work around. Like Hulu charges more if you pay via iTunes. Others do not allow you to pay via iTunes. Not really complicated.
I have HBO, Showtime, STARZ, Feeln, Netflix, Hulu, DIRECTV Now and more. I have paid some via iTunes and some directly to the the supplier like Hulu for different reasons and timing. I am also beta testing iOS and tvOS. I have seen SSO and use the New TV App (just to test). But I use a third party Universal Watch List called WatchAid which is much better for TV Series (no movies). Which also supports Netflix and pretty much everything else. I know how the TV App works where the WatchList comes from the App I really do not know which Profile Netflix would use. It would need to allow me to say when you are supporting the TV App please use this Profile to provide the watch list. Again, I am not a fan of the current version of the TV App but not sure Netflix is just not supporting them just because Apple is saying they must do something really strange. WatchAid has it own Watch List based on iCloud ID so it does not rely on the watch list from any App which I believe is how the TV App works. And the TV App controls it based on your iTunes ID and not your iCloud ID.