Firstly, because cloud contracts generally prohibit renting out the cloud services as-is - you can build a product on top of it but not act as a reseller of their platform.
Secondly, and perhaps most importantly because setting up separate LLCs with the goal of avoiding lawful debts is the demonstrates fraudulent intent and will get your LLCs veil-pierced.
You need to be a billionaire, and then you need to threaten to sue anyone who dares to ask you to pay.
Doesn't have to be as-is - a simple infra on top of it will do
> setting up separate LLCs with the goal of avoiding lawful debts
If normal bills are paid as usual and only this kind of crap is not paid, Amazon would have a hard time proving in court that the whole point of the daughter LLC was to avoid paying bills.