> And Nix doesn't?

If you're asking if installing/running software with Nix requires containers like Docker does: no, it does not.

> At least with Docker you can get something useful within 2 minutes

  % nix shell 'nixpkgs#ruby' -c irb
  irb(main):001:0> puts "Hello, world!"
  Hello, world!
  => nil
  irb(main):002:0>

That took me about 5 seconds to type out, and now I'm in an IRB REPL slinging Ruby code, despite having never installed Ruby prior to running that command. Add another 5 seconds for nix to fetch the necessary files (which are then cached locally, so a second `nix shell` invocation will be immediate) and we're sitting at roughly 10 seconds end-to-end.

If it takes 2 whole minutes to use Docker, Docker must be pretty bad. I guess vintage things have their appeal, but apart from that I don't see why people would be so attached to such archaic, inferior technology.

But is it pure?