What benefits do they get from running databases in Kubernetes?

Once you containerize every part of your application stack, you can simplify support/deployment to a single model, and you get the advantages of everything that containerization has to offer - dynamic scaling, robust recovery, trivial application migration, etc... without having to build in special rules/processes for one-off elements. The database then become yet one more component in your environment that isn't treated any differently than any other component - with the possible exception of requesting that it be scheduled less ephemerally than other components.

I've seen it work in production for 3+ years - And I don't recall there ever being an issue with the databases being in a container - it's hard to imagine them being anywhere else.

After reading that I start thinking everything would be better containerized. So why not run kubernetes nodes in containers?

You can!

KinD[0] is a project to do just that, although production workloads are an explicit non-goal.

[0]: https://github.com/kubernetes-sigs/kind

> So why not run kubernetes nodes in containers?

Plenty of usecases are already covered by that. Also, running containers in containers is also a thing.

It's containers all the way down.

Since the parent is running on GKE, they’re already doing that. Postgres in a (kube) container on a (GCE) VM in a (borg) container on a computer.