I like to look at Kubernetes as "distributed systemd".

"What if I could define a systemd unit that managed a service across multiple nodes" leads naturally to something like k8s.

Generally speaking, redundancy/availability could also be achieved through replication rather than automatic rescheduling, where you deploy multiple replicas of the service across multiple machines. If one of them dies, the other one still continues service traffic. Like in good old days when we didn't have k8s and dynamic infra.

This trades off some automation for simplicity. Although, this approach may requires manual intervention when a machine fails permanently.