Google tried with GAE, which is much closer to the Borg model (“I don't care about VMs, just run this code somewhere for me, and make it scale, make it automatically have access to a database”), but the world wasn't ready for it.
The world wants VMs and virtual networks and firewalls and clickable web interfaces and to run big legacy enterprise apps that MUST NEVER DIE and to fuck around with Terraform and to SSH onto boxes. This sucks, though, and Google SREs know better than to use such terrible abstractions unless forced to. The internal software development ecosystem is eons ahead of anything you can get with any cloud provider, but that sort of alien technology doesn't sell.
Kubernetes/GKE is a good compromise between something that Google sells but Google also wants to use. That, and some of the GCP versions of internal tools (Spanner, BigTable, BigQuery, ...).
