You can have thousands of packages in a single Nixos installation and if 200 of those packages directly or indirectly depend on some library L, you usually only

You can have thousands of packages in a single Nixos installation and if 200 of those packages directly or indirectly depend on some library L, you usually only need one copy of L to fulfill those 200 dependencies. In contrast, if you put each package in its own container or VM, then you end up with 200 copies of L. So, the different technologies have different strengths and weaknesses. One weakness of Nix is that it is harder for most people to learn or to understand than containers or VMs are. Some people use Nix or Nixos as part of their process for building containers or VM images. (I wonder whether there is any build system that uses containers instead of file names containing cryptographic hashes (like Nix does) or chroots (like Arch Build system does) to "enforce package isolation" during building.)