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).

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