I ran 1000+ VMs on a self developed orchestration mechanism for many years and it was trivial. This isn't a hard problem to solve, though many of the solutions will end up looking similar to some of the decisions made for K8S. E.g. pre-K8S we ran with an overlay network like K8S, and service discovery, like K8S, and an ingress based on Nginx like many K8S installs. There's certainly a reason why K8S looks the way it does, but K8S also has to be generic where you can often reasonably make other choices when you know your specific workload.