Nix is source-first, but with binary cache. Many things have to be installed again on non-NixOS because nix is hermetic - it can't use library X from underlying

Nix is source-first, but with binary cache. Many things have to be installed again on non-NixOS because nix is hermetic - it can't use library X from underlying system, it has to come from nix store. MacOS has issues with binary cache because of apple's requirement on where macOS can be run.