Why are frame pads no longer readily available?
From my perspective (normally a road bike user, and fairly good at falling of an MTB on rapid downhills) when I fall I always try to leave the bike, as pedals, cranks and sprockets hurt legs. 

So to me the most important things to protect are head, elbows, knees/shins and back. Frame pads aren't going to do anything for me, but protective clothing will.