Hardly a surprise. From what i have heard, it sounds like Google's internal use of GCP is mostly automated, using internal apis. I.e. it sounds like are not clicking through the screens, or even using the external version of the APIs. I question if the externally available screens are even capable of handling some of the special permissions that google internal workloads can be given.

This is in contrast to say Azure, where plenty of Microsoft employees are using the same resource manager APIs and even using the portal. I think even the billing related features get used as part of internal budgeting (they want teams to try to keep resource utilization reasonable). While teams developing parts of azure itself may be utilizing internal APIs (for example Microsoft Graph is basically just a giant wrapper around a variety of internal APIs), most of the rest of the company sees and interacts with azure in the same way we do. (Except that they also have access to dogfood/PPE environments that we don't, such that endpoints for say integration tests don't need to run on production azure).