Another reason is that us-east-1 has the most features and services and is usually one of the first regions to get new services. That is perhaps less of an ince

Another reason is that us-east-1 has the most features and services and is usually one of the first regions to get new services. That is perhaps less of an incentive now than it was a few years ago, and probably contributes to the instability in us-east-1, but if you need a newer service or feature that constrains your choice of region. And if once you've committed, switching to another region can be expensive.