Those things are never going to be adopted by Fedora, Arch, Gentoo, or any other non-Debian based distro. That is reason enough not to use it.
Then they are a small fraction of users but are not irrelevant.
very common scenario i come across few times a year: you get to work on an old CentOS/RedHat/Fedora box but you need to install latest package X which is only in next version of current distro. which would mean you need to upgrade or do a lot of manual work. with guix/nix you just install it without need to upgrade.