We could argue this ad infinitum, K8s of course doesn't remove all proprietary elements from a solution but it is a huge step up. Speaking as an ex-Googler, it took over 10 years but I'm so happy the rest of the world finally has a standard like this, the world is a better place for it even though I at one point had to unlearn all my traditional sysadmin habits and immerse myself in an environment practising it successfully to finally understand.
Your original question was what is the point. These are the points. As for why not Docker, k8s network effects and strategy of its sponsors mean Docker is on a lifeline, everyone knows that.
Of course Docker is doomed ;-) We have CRI-O, gvisor etc. showing that it works fine without it as well. Someone implemented a OCI compatible image runner in bash using standard cgroups, with a bit of luck we'll end up calling containers 'containers' and images 'images' instead of using docker's brand name.
Also, I'm not saying that k8s is bad, or using k8s as a practical API definition of the platform to target when packaging and configuring applications; I was aiming at the 'boo hoo k8s is too hard' tagline every "simple" version seems to hold on to.
One could also install standard K8S and remove the taint and run pods locally, same result.
Your original question was what is the point. These are the points. As for why not Docker, k8s network effects and strategy of its sponsors mean Docker is on a lifeline, everyone knows that.