The problem is that default.nix is like setup.py for Python. It allowed people do all kinds of nonstandard things and custom code. The callPackage pattern was d

The problem is that default.nix is like setup.py for Python. It allowed people do all kinds of nonstandard things and custom code. The callPackage pattern was developed later on, and people who use it as some kind of standard, but it was just one more "standard", also cli tools never were update to accommodate is, so that's why the complicated string is used. The flakes are essentially supposed to standardize it: https://www.tweag.io/blog/2020-05-25-flakes/ https://www.tweag.io/blog/2020-05-25-flakes/ (well their goal is to fix other issues, but the standard format of the file fixes that problem too and CLI supports it as well)