I don't know what's still true, but at one point us-east-1 seemed more critical than other regions because there were some things that had to be there. One thing that comes to mind is ACM certificates used with things like API Gateway (probably Cloudfront), they had to be in us-east-1 no matter where the rest of your infrastructure was.
So it's not shocking to me that something going down in us-east-1 could have impact on other regions.
So it's not shocking to me that something going down in us-east-1 could have impact on other regions.