Why options for non-admin programs in Nixpkgs and not Home Manager?

Nix allows users to manage their own packages without root privileges. it’s my understanding that configuration.nix is only for system-wide options, and i should use Home Manager for the rest as much as possible. why then are there so many options in Nixpkgs that seem like they should be in Home Manager? why is services.desktopManager.gnome.enable a system-wide option? it seems to have no equivalent in Home Manager? why is programs.sway.enable a system-wide option? is Home Manager’s wayland.w...