The image contains dependencies needed for 50+ languages. This means repls by default are packed with lots of commonly used tools. However, the image is massive, takes a long time to build, and is difficult to deploy.

Unfortunately, slimming the image down is not really an option: people rely on all the tools we provide out of the box.

May I ask why you didn't use something like Ansible to build such a complex image? With appropriate package version pinning (which it's the real crux here) it should work well enough to get a reproducible build.

I understand it would already have been something different from a pure Dockerfile so it's not that fair to compare buuut...

They did; it's called Nix, and they wrote a blog post about it ;)