Looking at what CloudFormation can and can't do it seems like completely different teams work on a service and its CloudFormation support.
I guess Amazon use the AWS API internally?
I say alleged because who knows if that's the code that's really running. And related to this current thread even if it is the code, with this being Amazon who knows if I ever found a bug and PR-ed it that it wouldn't /dev/null for 5 years before being closed by some stale-issue-bot or something
We dogfood both the SDK and CloudFormation internally, we just deal with its numerous gripes much the same way you would externally (although we can also contact service teams directly if needed).