Because k8s gives you lots of other things out of the box like easy scaling of apps etc. Harder to do on VM:s where you would either have to dedicate one VM per app (might be a waste of resources) or you have to try and deploy and run multiple apps on multiple VM:s etc.

(For the record I’m not a k8s fanatic. Most of the time a regular VM is better. But a VM isn’t = a kubernetes cluster).