Kubernetes is great when all your infrastructure is built around it, LXD and now Incus are great for when you have existing infrastructure that needs to keep on working. As in, turning physical systems into containers or VMs, running a local private cloud on your lab hardware, ...

Then when you want to deploy stuff with Kubernetes, you run LXD or Incus on your bare metal, create a bunch of VMs on it and deploy your K8s cluster on that, just as you would in a public cloud, but instead on your own hardware.