The dockerfiles are technically specified by OCI but the Moby project has a lot of sway in that committee. The Dockerfile spec has a number of deficiencies in it that aren't being addressed. Until recently, Docker was the only fully supported, ubiquitous way to build container images from a Dockerfile. The file even being called a "Dockerfile" is, in my opinion, annoying too.

Podman of course allows `Containerfile` but meh. I just don't like the tight coupling of the Dockerfile spec and the Moby project, since I don't like the Moby (Docker) project for the reasons listed above.