If one can get RSI in the wrists as a touch typist, why couldn't one get RSI in the shoulders or elbows as a 'hunt and peck' typist?

Because we don't move in a repeatable fashion. I'm not in one position, all the time. My whole arm moves in fairly random fashion.

The RSI is not because of movement, per se, it's because of repetition of the same moves (Thus, the "R" in "RSI").

Trained touch-typists keep their back straight, their arms at the same level, and basically only move their hands and wrists; always alternating between the exact same positions. I suspect that "extra-clicky" keyboards, which require a bit of force to actuate, don't help.

It's highly efficient, and I have always been in awe of really good touch-typists. Most don't get RSI, and I'm not sure what the difference is, with the ones that do.