Maybe there's a big difference between a rock shelter-type cave where the rock would be exposed to weathering, and, perhaps, already weakened (as seems to be the case with the site of the fatality referred to above) and a 'proper' cave (such as the Hard Rock Caf?)?
Incidentally, many years ago we were walking from Clapham to go down Alum Pot (heaven alone knows why, but we were . . . I guess it must have had something to do with being dropped off at a location that suited the driver rather the cavers) when we noticed what we took to be a column of water-vapour ? 'steam' ? arising from the vicinity of Bar Pot. We figured that there must have been some odd atmospheric conditions obtaining, that had caused relatively warm, moist air to rise out of the cave and then condensation to have occurred when it hit the outside air. So we walked over to have a look, only to find that it was a column of smoke. We decided to have a look down Bar, but got no further than the entrance, as we were driven back by the smoke ?we couldn't even tell if the cave was rigged or not.
So we returned the next day to find that the whole place reeked horribly of smoke, and there were the remains of a fire at the bottom of the big pitch. There was no obvious trace of anybody else in the system at the time . . . fortunately, as we had wondered if the fire-setters might have been overcome by smoke and we were about to find them down there. Maybe they just sat round the fire at the bottom of the pitch, and the cave acted as a huge chimney, taking the smoke out of harm's way (as far as they were concerned at any rate). We never did find out who had lit the fire, or why ? maybe someone thought they were doing a good turn by burning rubbish they had collected.