I don't understand this argument. Startups usually do not have money to have physical servers sitting around just waiting to be utilized, not to mention the IT resources to stand up those servers just in case someone might need them later. You're saying that everyone has a ton of servers sitting in the rack just waiting to have containers deployed to them? Who?
From k8s webpage (https://kubernetes.io/): "Automatically places containers based on their resource requirements and other constraints, while not sacrificing availability. Mix critical and best-effort workloads in order to drive up utilization and save even more resources."
Furthermore, running k8s to pack containers into AWS instances that are are themselves actually full blown VMs running on a hypervisor is of course one way to do computing. It is perhaps worth considering that there are others, more direct ways that can be achieved more economically.