Why do we do it?

Here's a grammar rule I've never been sure of (other than ending a sentence with a preposition, which I just did). Does one use the word "why" after "reason"? There doesn't seem to be any need for it, and yet everyone uses it.  For instance the visual above could just as easily read, "Forget all the reasons it won't work and believe the one reason it will." It even sounds better. Are we a nation that has been wasting millions of "whys" every year?  I say starting now we all stop using "why" after "reason" and if we don't, I'd like to know the reason why.