sorry if this is a stupid question, why would amazon only copy things hosted/using aws?
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.
Of course, Amazon could lie, but now if Netflix has a reason to suspect wrongdoing, they could sue.