Kubernetes is a big exception to this, it seems. Before Kubernetes was announced, CoreOS was actively developing fleet. After Kubernetes, fleet development was largely halted and is now just a "distributed init system for low-level cluster components," e.g. a way to bootstrap Kubernetes itself. I asked the lead developer of fleet if they would have created it if Kubernetes had existed at the time, and he said no. Kubernetes has turned into a big part of the CoreOS pitch, and they've contributed a lot to the project. Giving up a project you started in house because you recognized that another organization's project fit the bill better is very far from NIH.