If Amazon don't have a need to change anything in software, they'll just provide it as service without any problems. AGPL permits this.
If they have to change something, then they would likely want want to return hose changes in upstream to lower maintenance burden. Or just publish changes on github of upstream doesn't want to accept them. AGPL is fine with this too.
If Amazon would like create similar offering but with some secret sauce that they don't want to share, then they'll develop in-house solution from scratch and sell it as a service in AWS.
If they have to change something, then they would likely want want to return hose changes in upstream to lower maintenance burden. Or just publish changes on github of upstream doesn't want to accept them. AGPL is fine with this too.
If Amazon would like create similar offering but with some secret sauce that they don't want to share, then they'll develop in-house solution from scratch and sell it as a service in AWS.