...one is failure to use technological advances to make diving safer.
That is one of the problems with diver training today; technology is the answer to everything. In my experience, technology fails.
Other than the death toll....I would post a list of diving deaths with an END greater than 100ft from 1990 or so until 1997, but moderators deleted my post last time I did that (you can find it on aquanat archives). It was at least 200 names.
The problem isn't depth, it's depth coupled with a lack of experience and planning.
Having 2 wing inflater plugged in is a great way to have an uncontrolled ascent and not know which one to stop (or at the very least, delay your figuring it out).
You have it figured out before you get into an emergent situation. Again lack of training...