S3 buckets are a global namespace, so control plane operations have to be single-homed. As an example, global consensus has to be reached before returning a success response for bucket creation to ensure that two buckets can't be created with the same name.

The availability of CreateBucket shouldnt effect the availability of customers apps. This tends to be true anyway because of the low default limit of buckets per account (if your service creates buckets as part of normal operation it will run out pretty quickly).

The difference with Google Cloud is a lot of the core functionality (networking, storage) is multi region and consistent. The only thing thats a bit like that in AWS is IAM, however IAM is eventually consistent.

But isn't CreateBucket the single s3 operation where you need global consistency?

As far as I know bucket policy operations also require global consistency.