AWS IAM Policies: Why Don't Some Services Support Wildcards For Certain Fields In Arns?

Question

The AWS CodeStar docs say:

You can use wildcards only with the connection resources listed in the following table. You can't use wildcards with region or account-id resources.

But other services do allow you to use wildcards for region and account-id. What determines when wildcards can be used for these fields in an Arn? Any insight into how this works would be helpful. I don't see it in the doc on IAM identifiers.