I would never condone what this family did, but I think that I can understand how they happened to be in this situation and why there is serious problem with O/W divers entering cave systems or diving beyond the ability level.
I have been skiing all my life. I have taught a number of people over the years from their first days on ski's to some that had been skiing for some time. The same thing with diving. If you look at the learning curve for both of these sports, anyone that is just starting out skiing, knows the effects of bad choices. Everyone has fallen, they all learned quickly about steep and deep or ice, they can stop and look over an edge and know they won't make the first turn and it all hurts if you mess it up.
With diving, most of it is simple. If they have a reasonable amount of control over buoyancy, diving is easy. If you were to run a pole on SB, on how many divers in their first, say, 100 dives had a life threatening issue, I would have to believe it would be a very small number. They don't know what the dangers are. I know, they all have been told not to do this or that, but without having some experience with the negative aspects of thier choices, those warnings of will fade fairly rapidly. It's like training my kids or grandkids what "hot" is. You can tell them "don't touch, it's hot". But they have no concept of what it is until they experience it. I am sure that the entrances of these caves are a draw for these people that have never had a negative experience. For me, I had plenty of negative experiences diving over the years, so I knew not to tempt fate by entering one without the proper training.