Docker's codebase is a mess, the implementation is a mess, the data formats are a mess, the performance is a mess, it deadlocks under pressure (at least it did several years ago when I worked at Vercel), and I don't like its recent power moves to monetize people already somewhat locked into Docker.
But the dockerfile format has nothing to do with the docker codebase right? I run all my docker containers with podman (I recently moved over due to the monetization issues you mentioned), but I still use dockerfile format because they are (imo) good enough and also ubiquitous
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.
Just my opinions.