As far as I know, the attacks happened at different times. If Amazon knew that they had lost some data redundancy, shouldn’t they have been quickly mirroring that out of the region?
That would be a legal nightmare. They don't necessarily know what customers' data residency requirements are.
Most likely, their own data residency terms prohibit this. It would be interesting to know if, when 2 out of 3 AZs got destroyed, customers got a heads up to move their data to a different region?
https://aws.amazon.com/compliance/data-privacy-faq/
"You choose the AWS Region(s) in which your content is stored. You can replicate and back up your content in more than one AWS Region. We will not move or replicate your content outside of your chosen AWS Region(s) without your agreement."