At a certain scale, let's say 100k+ nodes, you magically run into 'it depends.' It can be kubernetes! It can be bash, ansible, and ec2! It can be a custom-built vm scheduler built on libvirt! It can be a monster fleet of Windows hyper-v hosts! Heck, you could even use Mesos, Docker Swarm, Hashicorp Nomad, et al.

The main pain point I personally see is that everyone goes 'just use Kubernetes' and this is an answer, however it is not the answer. It steamrolling all conversations leads to a lot of the frustration around it in my view.