Cavern diving is not all that dangerous. Bonne Terre takes novice divers into their cavern daily and they have a good safety record. Caverns are not overhead environments, and are not much different than a night dive. If you need to surface you can so how is that extreme risk? The answer is when one can get confused and enter a cave, hence the professional guide to prevent untrained folk from entering a cave in the first place.
Now the BASIC Discussion and New Area is inundated with messages from cave divers, BEWARE, you're not trained, bla bla bla. I for one am tired of these public service announcements from Cave divers in the name of safety. IMO if your foolish enough to go caving without training you may die. Its been beat to death, so I have to question are cave divers that bored?
You provide an excellent example of why cave divers need to continue banging on that particular drum.
As noted by a couple people above, your definition of "cavern" is seriously flawed. In addition to the open water distinctions made above, the cavern zone in a flooded or air domed cavern is defined by the ability to see natural light, and unfortunately that distance from the entrance can almost instantly shrink from a couple hundred feet to almost nothing.
Thus, even Cavern certified divers are trained to exit on the line they ran without any visual reference. It has very little to do with what you suggest - getting confused and entering the cave, but rather it can have everything to do with being able to see 100' to open water now, and then 5 seconds later not being able to see the light in your hand as anything other than a dim brown glow.
As noted above all caverns have air spaces at the top and while there are some "caverns" like that in Mexico, most are fully flooded, and in N FL I am hard pressed to think of any toursity cavern that has even an airspace at the top. Twin cave has some reasonably sized air bells, but we all know how close that cavern just came to being fatal for an OW diver, so I would not count on that as a resource in getting out of a cavern.
Similarly, a guide is not always the answer as just this year there have bee guided cavern dive fatalities in both MX and IT, and while it can be argued those guides may have exceeded the prudent limits of a properly guided dive, it does seem to happen with distressing regularity.
Yet you just told the entire board that cavern diving is not all that dangerous. Rather than suggest something derogatory, I'll just point out that you are not qualified to make that statement and maybe you ought to be quiet now.