Tons of examples where it works on developer's computer, but doesn't in production or someone's elses computer.

Dockerfile is not ensuring that build is fully reproducible, it's just list of steps to build the image. There are many issues with it, but biggest offender is due network access, if you're updating your package repo or downloading a file, there's a high chance that the resulting image is different every time. Dockerfile is as reproducible as a bash script. The only thing that's reproducible is the resulting image, but at that point so is a zip file.