French government moving towards using NixOS

I saw this yesterday and got pretty excited about it. It seems to me like this should attract more resources and developers to improving the Linux environment. What’s especially exciting in my opinion is the chance that France may contribute to hardening and improving the kernel itself, where a lot of the security vulnerabilities reside. There’s also a chance that other govs would follow, furthering that trend. I don’t fully understand nix, but I am curious why they wouldn’t just build their own packages and repo and use a more mainstream distro? Maybe nix really is that great?