Agreed. If Linux were a distributed OS, people would just be running a distro with systemd instead of K8s. (Of course, systemd is just another kubernetes, but without the emphasis on running distributed systems)
That whole concept is bizarre. It's like wanting to fly, so rather than buy a plane, you take a Caprice Classic and try to make it fly.
If CoreOS actually wanted to make distributed computing easier, they'd make patches for the Linux kernel (or make an entirely different kernel). See the many distributed OS kernels that were made over 20 years ago. But that's a lot of work. So instead they tried to go the cheap and easy route. But the cheap and easy route ends up being much shittier.
There's no commercial advantage to building a distributed OS, which is why no distributed OS is successful today. You would need a crazy person to work for 10 years on a pet project until it's feature-complete, and then all of a sudden everyone would want to use it. But until it's complete, nobody would use it, and nobody would spend time developing it. Even once it's created, if it's not popular, still nobody will use it (you can use Plan9 today, but nobody does).