My understanding is there's a pretty strong culture of running amazon.com directly in AWS as much as possible. I don't think there's much reason to believe a sectioned off alternative would be much more reliable, it would just break at different times maybe.

Possibly stems from one of the tenets of the apocryphal Bezos decree that started AWS[1]

> All service interfaces, without exception, must be designed from the ground up to be externalizable. That is to say, the team must plan and design to be able to expose the interface to developers in the outside world. No exceptions.

1: https://nordicapis.com/the-bezos-api-mandate-amazons-manifes...

That attitude, and the ability to enforce it at the scale Amazon is at, are probably the biggest strength of Bezos. It does cover all aspects so, including work culture...