See KEP in progress - kubernetes/enhancements#1985
dockershim has been part of kubelet for far too long. we vendor in a whole bunch of stuff from moby/moby to make things work. The correct split/ar...

Authors: Jorge Castro, Duffie Cooley, Kat Cosgrove, Justin Garrison, Noah Kantrowitz, Bob Killen, Rey Lejano, Dan “POP” Papandrea, Jeffrey Sica, Davanum “Dims” Srinivas
Kubernetes is deprecating Docker as a container runtime after v1.20.
You do not need to panic. It’s not as dramatic as it sounds.
tl;dr Docker as an underlying runtime is being deprecated in favor of runtimes that use the Container Runtime Interface(CRI) created for Kubernetes. Docker-produced images will continue to work in your cluster with all runtimes, as they always have.

This document goes over some frequently asked questions regarding the Dockershim depreaction announced as a part of the Kubernetes v1.20 release. For more detail on the deprecation of Docker as a container runtime for Kubernetes kubelets, and what that means, check out the blog post Don't Panic: Kubernetes and Docker.
Why is dockershim being deprecated? Maintaining dockershim has become a heavy burden on the Kubernetes maintainers. The CRI standard was created to reduce this burden and allow smooth interoperability of different container runtimes.