The problem is that a k8s cluster requires hundreds/thousands of lines of yaml configuration just for the core components, including a choice of network overlay. Everybody copies the same default configs hoping they will work out of the box, without understanding how each option actually affects the cluster. Add to this the container and yaml upgrades that should be applied per component every month or so, and it's nigh impossible for most companies to handle.

Kubernetes is far too complex to set up from scratch. The only way to reduce the complexity – or rather, to offload it – is to use managed Kubernetes via AWS or GCE. The fact that using AWS or GCE is effectively the only viable method for running a production Kubernetes cluster speaks volumes to how non-simple the stack truly is.