Why doesn’t need backstory. You need the /why/ to keep the reader to find out the /why/. Of course, if you can’t emotionally get the reader emotionally invested in the opening scenarios, then the /why/ won’t matter.
I think the clearer thing to say might be: You shouldn’t explain the Why with backstory, (No Lemming Talk) because you want to make sure the reader has a question that needs answered. The reader needs to be asking why. The writer already knows.
Author of Renn and The Springfield Chronicles