Kubernetes is also free software. So is Mesos. And Nomad. On the runtime side, rkt and runC are also free software. Just because something is free (and gratis)

Kubernetes is also free software. So is Mesos. And Nomad. On the runtime side, rkt and runC are also free software. Just because something is free (and gratis) software doesn't mean that people cannot complain and suggest improvements. That's how all free software development has worked since day 0.