See librarian generate PR googleapis/google-cloud-python#14576 which mentions No commit is found since last generation. Looking at the diff, there are changes since the last generation.

https://github.com/googleapis/google-cloud-python/blob/015634e3fe5c3305a49ad768f27c9e85c0f8e242/.librarian/state.yaml#L343-L345

  - id: google-cloud-alloydb
    version: 0.4.9
    last_generated_commit: 8cd780626041ecd4666974fd0c4099f1ad1ca01a

The latest commit is 8cd780626041ecd4666974fd0c4099f1ad1ca01a which includes changes from

googleapis/googleapis@8cd7806
googleapis/googleapis@48c3f2f
googleapis/googleapis@fc225fe

We're also seeing this issue in google-cloud-go where googleapis/google-cloud-go#12959 contains changes for dataproc which are not captured in conventional commits