I agree that guided cavern dives are very similar to DSD dives. And in both cases, for many reasons, right or wrong, they are not about to disappear.
Also, I find that saying "he (the victim) didn't belong there, he dived beyond his training, etc" is being too simplistic and obtuse and misses an opportunity to improve on the safety of the activity, and maybe help in the conservation of the access to the caves for all divers.
Last time a cave accident happened in Mexico it caused a loss of access to some caves for all divers and the need to have a local guide even for trained cave divers in other caves (even if the accident was a guided cavern dive with a local guide).
IMHO, as a guide with DSD students, you cannot expect the customer to know everything and or to do everything perfectly. I think there should be a very thorough briefing before the dive, and constant attention to the divers through out the dive. There should be comprehensive liability waiver forms to be read and signed before payment for the dive.
After all that, the divers should understand and accept responsibility that they could very well die if they don't follow the instructions and the guide. And that the kind of dive they want to do incurs more risks than a normal dive.
That being said, and I think this might not please some people, I believe the problem lies in the guides and dive shops in Mexico.
As:
-A lot of the guides give lousy briefings.
-A lot of the shops don't give a realistic idea of the dive to the customers.
-A lot of the guides take divers of insufficient skills to those dives.
-A lot of guides don't follow the cavern lines close enough, as they know the way and they don't think about the fact that the customers might need that line.
-A lot of guides take customers into the cave zone, beyond the reaper signs, in the hopes of receiving a bigger tip, or for their own enjoyment of the dive, as some get bored of doing the same caverns all the time.
-Some people remove the reaper signs, so customers don't realize they are out of the cavern zone and into the cave.
Please note that I wrote "A lot", as it is very common. Like in every day.
But, there are a lot of shops/guides offering cavern dives and some of them are as professional as can be. Some of them are the ones putting up the reaper and cavern signs, giving quality education and helping all divers with having good relations with the authorities and the landowners.
So, in short, I believe the only way the situation is going to get any better in Mexico is with better education/enforcement of the accepted practices to the dive shops/guides. Sadly, I don't think it's happening anytime soon.