Of course they don’t use layer upon any of their own services.
Otherwise what would they do when they inevitably get discontinued?
Not so long ago (a few years), Amazon retail was not using AWS either (I think they do, at least partially, now).
Well, the problem with Google is that AFAIK they have no plans to onboard their important services like Search onto GCP. I believe a few years ago they have tried but found the GCP tools too lackluster for internal use.
This is true and false. Google services, including GCP, run on its internal cloud. GCP is just a product on top.