Can’t use cloud stuff on-prem and also if your clients have a server room of their own. Same for homelab.
Also it’s nice not to shift the pets attitude from servers to clusters and instead treat everything as cattle - provided you have backups of persistent data and the config versioned in a Git repo and there’s maybe some Ansible in the mix, being able to recreate an environment in the case of a fuckup is nice and also helps against bit rot.
Disclaimer: I actually prefer Docker Swarm/Compose over K8s due to simplicity (which matches my deployments and scale), but in the cases where I had to use a variety of K8s, going for K3s was pretty okay.