Of course lots of AWS services have hidden dependencies on us-east-1. During a previous outage we needed to update a Route53(DNS) record in us-west-2, but couldn't because of the outage in us-east-1.
So, AWS's redundant availability goes something like "Don't worry, if nothing is working in us-east-1, it will trigger failover to another regions" ... "Okay, where's that trigger located?" ... "In the us-east-1 region also" ... "Doens't that seem a problem to you?" ... "You'd think it might be! But our logs say it's never been used."