Amazon likes to diversify their payment processors. They don't have one payment processor for one region because it's an availability issue for them. Cost of payments is big. So this is likely some agreement to help Amazon reduce their cost of payments, by essentially redirecting costs to the AWS side of things. India likely isn't being processed because India has regulations that most other countries do not. Adyen, Braintree, and maybe not even Stripe can be payment processors there (if they are, they're likely just a proxy for another processor).