There is no service with 100% availability. You put multiple AZs in one region but nobody was ever pretending that regional failures were impossible, just that single-AZ failures are more common than regional failures. You want high availability, you want multi-regional. Above that you want multi-provider.
The same decisions that make regions fail also makes infra-region traffic cheaper. This is true for all large cloud providers. If you are okay paying more for internal network traffic you can get multiregional. But multi-AZ is still better than single-AZ. Up to you to decide if it’s worth it. For that you need good SLAs and (IMO) support contracts.
