I think it’s trying to set you up to increase your chances of not having new bucket name denied.
There’s still no guarantee the name won’t be taken, but using your account as prefix helps this.
Working with Amazon S3 Buckets
An Amazon S3 bucket name is globally unique, and the namespace is shared by all AWS accounts.
Bucket restrictions and limitations
A bucket is owned by the AWS account that created it. Bucket ownership is not transferable.
S3 compatible (Minio) bucket name convention? points out this doesn’t fit private installs. Is yours one?