> which is the standard for all of Google's public APIs
Far from that, unfortunately. A lot of Google public APIs predate AIPs and it's practically impossible to fix them and make them compliant. Possibly the worst offender is the Compute Engine API [1], which, to the best of my knowledge, is REST only (no gRPC), uses its own conventions related to page size / next page token, and, in general, is special in many ways. One of the ways it's special is its size: its definition in Google's own Discovery format [2] is a 6MB JSON.
It's an extremely difficult problem to standardize multiple APIs produced by multiple teams, and then keep the new changes compliant. Google did a great job, but it's still very far from the perfect state.
[1]: https://docs.cloud.google.com/compute/docs/reference/rest/v1
[2]: https://www.googleapis.com/discovery/v1/apis/compute/v1/rest - warning: 6 megabytes JSON
[edit: typo]
