This always bites me. I wish it could be opt out. I'm fine namespacing my s3 buckets with my region and account and I rarely ever use s3 domains
Internally at Amazon people are expected to spin up entire separate AWS “conduit” accounts for different environments. So this only applies if you’re running everything out of one account, which is bad form.
To their point, S3 buckets must be uniquely named globally, across all of AWS