AWS can see traffic and usage. They can predict the "next big thing". Facebook allegedly did the same with their VPN services that analyzed what apps people were using on their phones.
Of course, Amazon could lie, but now if Netflix has a reason to suspect wrongdoing, they could sue.
This isn't how the world works.
And the example of Facebook with Onavo is also not plucked out of thin air[0].
Sure, it's not how all of the world works but for the big players, it's a important tool in their toolbox.