does not entitle you to do whatever you want and tell people to "make their own thing" if they don't like it.
He not only wrote it but made it open source so if anyone doesn't like what he's doing they can take all of his work and make their own project.
The author of NixOS couldn't have been more generous. If anyone doesn't like it, they can take all his work that he did for free and make it their own project.