Nix is for people who have entirely given up on the idea of system libraries. There is no system. Unless someone else has already done the work every single random bit of .c code, or whatever, you try to compile or run will require you to explicitly set the system libaries available/required to run it in a set of config files. It's like building a custom OS container for every single program you run.

For some people this is good because future shock has made relying on system libaries to run things very troublesome. So troublesome it compares to the above.