I’m not sure I see the problem here? It does say most cases and I’d definitely consider Nix/GUIX users to be in the minority for this (on top of users who would even compile software themselves in the first place).
Also from what I experienced during my (not so long) time with NixOS, usually things in Nixpkgs were contributed there by community members who ported applications over to be compatible with Nix. Sure, it’s a nice extra thing when the application developer does so out the gate, but given how special Nix and GUIX’s environment is, the onus has never really been on the app dev.