One reason is probably that people don't know about them.

1. As you can see from the state of this thread, people see nix or nixpkgs but read nixos. There's no momentum from the community to push it as an extra package manager, while every thread is spammed with nixos.

2. No gui integrations for casuals. For example Discover integrates flatpaks and snaps, but for nix you need to use the terminal.

3. The documentation is abysmal. I spent days trying to figure out how to use nix as a declarative package manager before I accidentally came across home-manager. Even the manual leads you down the wrong path. A quick start guide with a few examples for home-manager and flakes, and a few basic commands, would've had me going in 5 minutes. That problem is made worse by the fact that almost all sources of info focus on nixos instead.

Edit:

if anyone's interested in trying it out, here's a part of my other comment in this thread

It's just a list of packages, and an optional flake to control the repositories (stable/unstable) and add packages from outside of the official ones.

To update everything nix related I just run:

cd ~/dotfiles/nix/ && nix flake update && home-manager switch

Because it has abominable documentation. Some tools built on top of nix on the other hand have stellar documentation (devenv and jetbox come to mind). The tools even try hard to hide nix because they know it's a goddamn nightmare for beginners to use it.

The CLI is a mess due to the indecisiveness of the nix maintainers whether they want flakes or not. So much so that the official manual doesn't use flakes, but many guides on the internet immediately go into nix dev#yadadada which leaves beginners and mid-term users alike very confused.

Another point is that graphical applications can't use OpenGL without dirty hacks like nixgl. Not only that, installing GUI applications using nix doesn't make them show up in your desktop environment (start menu, finder, whatever). No, you need to either manually create .desktop files or install another tool like home-manager to have them show (and not work properly because of OpenGL).

To top it off, unless you know better, it's command-line only. SnowflakeOS is building GUI tools around nix, but they aren't like say Discover or the Gnome Appstore: you can't install the GUI and have everything working - no, you need to figure everything out.

In short, nix is absolutely nowhere close for desktop user adoption, much less mainstream linux adoption (dev, sysadmin, tester, or whatever other technical role exists).

CC BY-NC-SA 4.0

Learning curve? I've meant to get around to it but my to do list is pretty big so far.

Nix is on the destinations to visit but the configurations are still confusing at a glance.

I'm going to go against the grain and say that the Nix and Guix package managers are very good, but they really belong in their respective distros where they're a core part of the system. That'd be Guix System for Guix and NixOS for Nix.

They may have advantages for a foreign distro too, but they are lesser (Guix System can boot into a backup of the system before the last update, for example, but that advantage doesn't exist on, say, Debian.

Also, can we agree to not recommend these systems to new users for the time being? While they're very powerful, they're absolutely designed for power users, and until they're more polished and they have fancy GUIs and stuff for installation and package management, I think it'd be best to keep recommending normal distros like Debian for now.

Nix packages are a pain to manage on non-nix systems and basically all documentation exists for nixos, not nixpkgs.

I maintain some software, and Nix is by far the hardest to deal with. To package config files are relatively complex, and to submit a package you have to download the entire Nix repo, which is huge. Getting a package to build correctly can be a challenge.

It's a pretty large ask for software contributors, who may have to iteract with a half dozen different distros. Now, you could say, leave it to the distro people to do the packaging, but it remains a barrier for entry and is by nature exclusive.

I don't use NixOS, so I have little motivation to stay conversant with Nix and, frankly, it's so demanding I don't bother anymore. I can make RPM, deb, and aur packages trivially, and without having to hold Gb of some package repo (which I otherwise don't use) on my disk.

the aur has everything I need

Part of the reason is that people are still finding out about it, Project has no marketing so it grows organically, in the last year the number of contributors grew by 25 percent.

Another problem is that it still needs polish in term of ease of use, for example it takes me forever to search for packages using the nix-env command but using the website it takes less then a second, That's a basic feature that still does not work correct, Plus their documentation is still not great in my opinion, I actually helped improved it and the improvement they made is still not really good IMO.

The way nix installs in my root directory in another distro is a no-go for me

For me personally, I just haven't taken any steps into the nix environment. Seems rather complex, setting up those nix files and stuff.

I use Debian on servers and LMDE on my PC, most things I need are in the Debian repos and for other cases I get by pretty good with appimage s and flatpaks. Installing is just a simple command and me happy.

Nixpkgs are probably easy too, I assume. I know a lot of people really like nix, but the effort required to start seems significant to me, especially when we have other methods that just work.

You're not exactly comparing apples to apples here.

Flatpak and appimages tend to be used in any distro because they can just be downloaded in a one off manner and installed then you're running the application (for the most part). They offer a manager of sorts but you don't need it to use the packages.

For nixpkgs, whike I'm sure I can get a package from the sounds of the sizes the package covers only the application or the library, meaning I still need the dependencies.

So what exactly would make me the user trade my built in tools (apt/pacman/dnf) for nix? Keep in mind no matter how great you feel it is, you need to provide reasoning that motivates me to install and learn this new tool instead of the old ones I have.

Pacman (and paru and the AUR) and chezmoi works fine, I don't see any reason to switch.

yeah, everybody should use them. I usually write my own kernel mods tailored for my hardware and certain needs, I don't know why not everyone is doing that. admittedly is a bit janky maintaining a separate kernel fork, but you get used to it, everyone should do it

I use NixOS on my personal machine and nixpkgs on my work Ubuntu (22.04 LTS). In the absence of NixOS I would not be using it: it somehow breaks all the file (open, save, etc.) windows, causing any app that tries to open one to crash (particularly annoying for browsers).

Not to mention the wrapGL issue.

It needs more polish on "genericlinux". I did previously use it on MacOS, and it did make MacOS almost bearable - definitely years ahead of brew.

NixOS sounds amazing in some regards, but I'm not really interested in learning a whole programming language for it... I have enough to do already.

Inate complexity that keeps moving as they introduce things like flakes.

Its a declarative configuration management system as package manager. Thats a lot more to handle off the bat than normal linux + flatpak.