In the coming hours/days we'll find out if AWS still have significant single points of failure in that region, or if _so many companies_ are just not bothering to build in redundancy to mitigate regional outages.
I'm looking forward to the RCA!
A lot of AWS services under the hood depend on others, and especially us-east-1 is often used for things that require strong consistency like AWS console logins/etc (where you absolutely don't want a changed password or revoked session to remain valid in other regions because of eventual consistency).
even internally, Amazon's dependency graph became visually+logically incomprehensible a long time ago