OCI image repositories are pretty ubiquitous nowadays and are trivial to setup.

I am sure that a lot of people have them deployed and don't even realize it. If you are using Gitea, Gitlab, Github, or any of their major forks/variations of you probably already have a place to put your images.

So I really don't know what the advantage of 'single file distribution model' is here.

This is probably why people don't bother sharing tarballs of docker images with one another even though it is has been a option this entire time.