Because "learning" Erlang is like learning any language. Sure, you can learn the language in short period of time, but really being able to professionally support a production level app to the level needed will take a long time and a lot of practice. And that practice isn't a week long course where you suddenly learned Erlang and then that's it. You aren't working with Erlang any more.

You don't need someone "learning" Erlang. You need someone who works with it.