> 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.