Who knows, but I always attribute the term to either the fact that you effectively have to come to a stop before the issue resolves or my favorite is the death of the suspension design on a built rig. First time I ran into Death Wobble back in the 90's was when I had a guy bring his hugely built Jeep with 44's in to have me solve the death wobble. The Jeep was a mess though. Death wobble is nuts with 44" super swampers. Both versions are my own interpretation and preference for the origins of the term though I'm sure neither are right.
As for accidents, I certainly almost ended up in the wall on the Dallas North Tollway when I first had Death Wobble on my IG. It was pretty gnarly. Im sure there have been injuries that could be attributed to Death Wobble but it's not a major concern otherwise Jeep and Ford would have been sued out of existence. Along with some others I would guess.
But soiling pants is probably a pretty common occurrence as a result of Death Wobble.