Here's the straightforward version of why I use it:

1. The entire state of your operating system is defined in a config file, and changes are made by changing the config file. This makes it super easy to reproduce your exact system many times and to know where all the many different configuration elements that describe your system are located.

2. Updates are applied atomically, so you don't have to worry about interrupting the update process and if it fails, the previous state of your system is still bootable. By default every time you change something, you get another option in the boot menu to roll back to.

3. Making container-like sub systems is super easy when you're familiar with nix, so you can have as many different enclaves as you like for different software versions, development environments, desktop setups, whatever without taking a performance hit. Old versions of stuff are very accessible without breaking your new stuff.

4. The package manager has a lot of software and accessing nonfree stuff is straightforward. Guix looks rad, but nix ended up being the more practical compromise for my usecase. I didn't want to have to package a heap of software the moment I made the switch.

everyone

Now that's what I'd call a stretch...

It's in no way "everyone", just a vocal minority.

I used NixOS for a couple of years. My experience is like this:

1. It is a rolling release (mostly)
2. You write a declarative configuration for your system, e.g., my config will say I want Neovim with certain plugins, and I can also include my Neovim configuration
3. It is stable, and when it breaks it is easy to go back
4. Packages are mostly bleeding edge

It's insanely stable but you have to have a lot of linux/programming knowledge to do even the simplest things like installing/updating your software or making little tweaks. I played with it for hours the other day and I'm just too dumb to figure it out lol I think it's just a super stable highly customizable distro for power users and a lot of people like that. If you can get over the learning curve it's a pretty powerful and unique os

I daily drive GNU Guix instead, and I would strongly recommend any emacs and/or lisp enthusiasts interested in the benefits of functional, reproducible, declarative, and hackable system management to give it a try!

I have been using for years on servers. My lemmy instance is hosted on it.

Although for desktop I had too many issues back in 2019 so I ended up back to Arch Linux and then EndeavourOS

Would be fun to try again to use it on desktop

NixOS is a fully declarative and reproducable system.

What this means is that you can create a single configuration.nix, which includes all of your applications, settings, aliases, environment variables, user account + groups, etc., and copy that over to another NixOS machine (including different architectures) and run nixos-rebuild boot to completely reproduce the system on that other machine.

The nix package manager is also really good at telling you if the configuration will break anything, where, and how, and refuses to apply until the issue is fixed.

Also every time you use nixos-rebuild, it creates a new generation of your NixOS install meaning if something ends up breaking, you can reboot into the old system.

So for example, I can theoretically have the exact same configuration across my desktop, laptop, phone, server, etc., minus the automatically generated hardware-configuration.nix, which is specific to the hardware.

Also Nix supports package overlays, which means that you can modify an existing package while the maintainer still keeps it up to date.

I've been using it for over a year and love it. A config file for your entire system, and built in rollbacks anytime something goes wrong. One language to configure everything, although in practice that doesn't always work. But I love it.

Some others have started why it works, here is some how. Nixos completely disregards the fhs. Packages don't install to anywhere standard, every package and configuration change gets it's on directory in /nix/store but through smart use of tracking everything there, it symlinks all those files to proper places and sets up the environment for them to know where libraries are.

This is then also why you don't need sudo privileges to install things. Your profile has an environment that is aware of your users packages and configurations, the system itself isn't effected because everything is symlinked.

Then because every update means new directories in /nix/store you can role back to your last configuration because plasma broke something or whatever.

However, it's a LOT to learn. Best place I know of is https://piped.video/watch?v=AGVXJ-TIv3Y&t=0

This guy did a good job for me. Hope this helps!

Overlays. Good package management, and lot of stability stuff.