Yes, that disparity has long been noted.
I live in a rock climbers paradise, and several people are killed climbing each year. I have never heard of anyone calling for the cliffs they were climbing to be closed. Yet, as has been noted, there have been more than a few cases of caves being closed when a diver dies in one.
One major factor is that many and perhaps most of the dives in the world are done off of boats, and those boats are owned by operators who take you out and manage the dives for you. Those operators can be sued if there is a fatality. That leads them to do what they can to make sure that the divers they carry have the necessary ability to do the dives safely. It would be impractical to test everyone before the dive, so they rely upon certification, and for the most part, that certification will protect them in court.
Many people do not realize that the boat operators are governed by laws, and those laws require them to meet certain standards of protection for those divers. You will see many people post on ScubaBoard that a dive boat is just a taxi with no legal obligation to the divers they carry, but that is simply not true. We are seeing that these days in the cases of the burning boats, but it happens in other ways. For example, a few years ago a diver went into distress (likely cardiac event) on the surface, struggled there briefly, and drowned. The boat captain was cited and penalized by the coast guard for not being on the deck supervising while divers were entering the water and for not training the crew on standard lifesaving techniques. It turned out that a diver struggling in the water is a man overboard, and the crew is required to follow standard procedures for such an occasion.
