It's confusing, but Docker images (and image registries) are also an open standard that Docker implements [1].
A lot of the Kubernetes "cool kids" just run containerd instead of Docker. Docker itself also runs containerd, so when you're using Kubernetes with Docker, Kubernetes has to basically instruct Docker to set up the containers the same way it would if it were just talking to containerd directly. From a technical perspective, you're adding moving parts for no benefit.
If you use containerd in your cluster, you can then use Docker to build and push your images (from your own or a build machine), but pull and run them on your Kubernetes clusters without Docker.
A lot of the Kubernetes "cool kids" just run containerd instead of Docker. Docker itself also runs containerd, so when you're using Kubernetes with Docker, Kubernetes has to basically instruct Docker to set up the containers the same way it would if it were just talking to containerd directly. From a technical perspective, you're adding moving parts for no benefit.
If you use containerd in your cluster, you can then use Docker to build and push your images (from your own or a build machine), but pull and run them on your Kubernetes clusters without Docker.
[1] https://en.wikipedia.org/wiki/Open_Container_Initiative