K8S based on distros like k3s or microk8s is a great and simple solution for manufacturing and managing edge devices, IoT solutions and similar products that are setup once on a single box that runs half a dozen or more things and are shipped to business clients.
It is very simple to spin a minimal distro based cluster. It is relatively simple to have it up and running your solution. Sure getting Kubernetes from the source and tailoring all the required components to run cluster with full HA etc' is a complex stuff, but building a private cloud based on vanilla Kubernetes isn't the only or the most common use case.
I've also seen more of it being used for deployments of on-prem versions of SaaS services. I think the idea is that if you're already hosting your SaaS services on k8s distributing a machine image to your Enterprise customers running a scaled down deployment of your services on a single node kube cluster makes some of the packaging and updating challenges easier.
It is very simple to spin a minimal distro based cluster. It is relatively simple to have it up and running your solution. Sure getting Kubernetes from the source and tailoring all the required components to run cluster with full HA etc' is a complex stuff, but building a private cloud based on vanilla Kubernetes isn't the only or the most common use case.