Risk is one thing (and I don't think you could pay me enough to get into a "commercial" submarine for a tour a couple of miles below the surface). If they cut corners, the risk could go from a tiny possibility to an almost guaranteed disaster. I wonder, if you told the people paying such large dollar amounts that they might not be able to track the sub if it got lost, would they have stepped aboard?
I don't know anything about deep-sea diving or the capabilities of tracking technology two miles down, but if you told me "you've got around 40 hours of oxygen, and also if you get lost we probably can't find you" I'd have asked for my money back on the spot.