Another way to look at it is that Google has a batteries-included opinionated way to deploy internal services, it would be an incredibly tough sell to off that more directly to other users. "First rewrite your app in one of these 4 languages" doesn't fly. People want to buy a VM, or maybe a Kubernetes cluster.
(Plus external services need stronger tenant isolation which Google internal services don't deliver)
(Plus external services need stronger tenant isolation which Google internal services don't deliver)