Google Cloud Platform has its own domains product called Cloud Domains. https://cloud.google.com/domains/docs/overview

Google has had a big problem for over a decade with having multiple overlapping products, leading to wasted effort and customer confusion. It also leads to a bunch of extra work when one product is rolled into another or shut down.

It's unclear to me why they didn't migrate everyone over to GCP Cloud Domains. I'm also not sure that most customers really care if they're using Google Domains vs another registrar vs GCP Cloud Domains.