What I've seen more than anything else is that Kubernetes built an ecosystem (of contributors and users, but also of
companies invested in its success) that none of its competitors could or would. There was apparently a faction within Google that believed open-sourcing Kubernetes was a mistake because Google would have made more money keeping it in-house, but in terms of the success of the
project I think it was entirely the right call, as was creating a foundation to maintain and promote it. Look at the history of its competition:
* DC/OS was always its own thing and as time went on, eventually Mesosphere was basically the sole maintainer of the underlying Mesos. Very little external contribution.
* OpenShift was different from Mesos and basically maintained only by Red Hat from the Makara acquisition (sometime in 2010 I think) to about mid-2015 (i.e. the point where they ripped out most of the OpenShift-native process isolation and orchestration and replaced it with Docker and Kubernetes). Pre-Kubernetes OpenShift frankly struggled to catch on and again, basically everybody who cared about developing it worked for one company.
* CoreOS was developing fleet in the open but dropped it outright when Kubernetes was released. The phrase I heard there was "We started to say something and Google finished our sentence." They pivoted to Kubernetes for orchestration so hard it was kind of awkward talking to customers who used fleet after that. In theory somebody could have picked it up like Kinvolk picked up rkt for awhile (and later CoreOS Linux as Flatcar), but as far as I know nobody ever made a serious effort to do so.
* Docker released Docker Swarm shortly after Kubernetes was released -- yet another one-company product. (I still don't really understand why they released Swarm -- for simple workloads, Docker Engine and Docker Compose were enough, and for more complex ones Docker Engine was, at that time, still the sole underlying runtime in Kubernetes. There were already two distinct orchestrators on the market, one from a much larger company with a lot more operational experience running containerized workloads than Docker had. What was their thought process?)
* HashiCorp released Nomad well after Kubernetes but not only was it another sole-corporate-maintainer orchestrator, it deliberately omitted a lot of the basics Kubernetes included like service discovery in an effort to stay simple -- so in very few cases was Nomad alone actually enough to orchestrate workloads (nor was it intended to be, as the Nomad engineers in the ~1.0 days would have been first to tell you). Past a point this made Nomad more work to get running and keep running than Kubernetes was.
The flip side is, I don't think a purely community-developed orchestrator would have won, even with a foundation backing it. It's not the corporate backing that's the issue, it's the lack of diversity in that corporate backing.