How do you run multiple copies of an application? How do you start new copy when one fails? How do you deploy changes to the system? That is the orchestrator.
What do you do when site gets really popular and needs new copies? What happens when fill the VMs?If you want to automate it, that is a controller.
Also, if you are running on-premise, you don't need VM, you can use the whole machine for Kubernetes and containers for isolation. If you need more isolation, you can run VM containers; being able to switch is advantage of Kubernetes.
What do you do when site gets really popular and needs new copies? What happens when fill the VMs?If you want to automate it, that is a controller.
Also, if you are running on-premise, you don't need VM, you can use the whole machine for Kubernetes and containers for isolation. If you need more isolation, you can run VM containers; being able to switch is advantage of Kubernetes.