Companies looking to make money in the world of Linux went out and took the core, bundled it up with their best practices and their favorite applications, and then sold it as a “distribution.” You see this with Red Hat Linux, Ubuntu, etc. — even the open-source versions took the base system and then built significantly above and beyond that to the point where each had its own default windowing interface, and some were massively different experiences for the user even though what was underneath was basically the same.
The business model was opinions, applications, user experience, security and support, all wrapped around the Linux Kernel. This worked great, and at least a few companies built large, successful businesses on top of this model. It worked so well that there are several companies looking to do the same thing with Kubernetes.