Are you kidding? Half of NixOS is written in bash.

Nixpkgs is just Nix used as a metalanguage for splicing together bash object language programs.

Guix is what it looks like when you really get away from bash -- they use scheme as both the metalanguage and the object language.

The caveat is that you're pushing the complexity somewhere else. I'm finally moving away from NixOS this month (after two years of using it) because I'm tired of edge casing interrupting my daily flow.