Stick pushers are normally fitted if when an aircraft reaches a critical AoA the tailplane/elevator ability to unstall the wing is compromised. The classic example is the 'T-Tail' design where tailplane/elevator blanking occurs at high AoA and the aircraft cannot be recovered from the stall. It is essential on those aircraft and PREVENTS the pilot getting into the 'deep stall' by forcing the stick forwards and thus reducing the AoA. I'm not sure when they first flew, but I think it was following the BAC 1-11 crash in 1963 which killed Mike Lithgow and crew which was, I think, when the tail-blanking event was first recognised..
Would it be good not to have it interfere with a pilot's death wish? It should only work when the pilot has screwed up - as per your last sentence! As for how many push events there have actually been, I know not.