It’s the “original” AWS region. It has the most legacy baggage, the most customer demand (at least in the USA), and it’s also the region that hosts the management layer of most “global” services. Its availability has also been dogshit, but because companies only care about costs today and not harms tomorrow, they usually hire or contract out to talent that similarly only cares about the bottom line today and throws stuff into us-east-1 rather than figure out AZs and regions.

The best advice I can give to any org in AWS is to get out of us-east-1. If you use a service whose management layer is based there, make sure you have break-glass processes in place or, better yet, diversify to other services entirely to reduce/eliminate single points of failure.