have we completely diverged from the original question or is that one still in play? my take on the original question was that the cave diving environments envisioned tended to be more stable, so barring an earthquake or something like that - the cave isn't changing much aside from a silt out. So the dangers in the cave could (to some degree) be worked around by throwing hardware and planning at the problem. Redundant air, redundant computers, redundant CCR, etc. You can personally plan your risk level.
Whereas you could take all that planning to the ocean for a boat dive, and you surface to find the dive boat decided headcounts are for losers and now you're drifting out to sea, sharks decided they have a rubber fetish, or recreational boaters not even noticing flags/divers in the water. What random dangers in the cave? guide lines breaking off their anchors while you're down the hole, or having someone remove your ties?
It seems the cave risks can be planned for with an extremely pessimistic approach to the dive, whereas the open water dangers can't as easily be mitigated by your own proper planning/preparation. Your danger is how optimistic you are.
(otoh a surprise medical episode in open water they can likely shoot to the surface and to help faster thsn hauling you through a tunnel... swings and roundabouts. I can see why someone feels safer knowing they planned away the dangers of equipment failure, versus not knowing if the danger was a gaping maw headed at you in the murky vis)