And then you didn't mention the whole concept of storing everything in one-huge-always-expanding-blob ~/Library/Containers/com.docker.docker/Data/com.docker.dri

And then you didn't mention the whole concept of storing everything in one-huge-always-expanding-blob ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2 file which contains all Docker related storage, images, data volumes etc. Now that file just loves growing to 40 GB+ and there is no supported way to reclaim that space. You can delete the file (or click Reset to factory defaults in the GUI), but then you loose all your Docker's storage, like data volumes.