It is easier because you can actually build that functionality locally with a docker container to test it out.

This is coming from someone that spent 10+ years maintaining a build system that was a mix of makefiles and shell scripts. It can be done but I don't know if it should.

Because a Docker config makes it hard to accidentally wipe your filesystem instead of building a Docker image. Shell scripts make that less difficult (and any solution using shell to do something similar to Docker will have a bespoke layer of in-house code that should be correct but will require maintenance by your team to make sure nobody makes a change that turns it into a filesystem-eater).