The pickaxe guys coined it. People repeat it without thinking about it.
If matz were to say "jump from the bridge", people would do it, because matz is nice?
Just to point out: I do think matz is nice and a great language designer. That in itself doesn't mean anything. Why would I proxy my own decisions based on any mindless slogan? That makes no sense. Why do people in the ruby ecosystem keep on repeating those pointless slogans?