It's a good move for netflix because
- side step net neutrality rules. If it's likely a tier one carrier will screw over your traffic, just store the important stuff with the tier two carriers...
- AWS is pricey what we way you look at it, and network costs can only go up. Amazon is a prime (!) competitor for streaming and it's a bad idea to put all your eggs in your competitors basket
- Disney is coming over the hill. They have great content - i mean insanely great. But I bet Disney sucks rocks at hiring network SREs. They will get there eventually but if you want a huge differentiator between you and the House of Mouse, being the one without a spinning egg timer is pretty good - especially as there is no chance you can match their content.