Wait, obviously Amazon has their own checkout software. Is this a name recognition play to have AWS come with Stripe batteries included?
They do, but Stripe may have other advantages that Amazon's home-grown billing does not... fraud detection comes to mind.
Stripe's superior fraud detection is an open secret in FinTech. There are apparently a lot of large companies with their own payment rails that route riskier looking payments (e.g. a new account who you haven't yet settled a transaction with) through Stripe for this reason.
which probably makes stripe's job even harder, because now there's adverse selection