People rarely decide that "today is the day I'm going get killed diving". They normally just fail to understand how dangerous what they are doing really is, often because they have gotten away with something kind of like it before. It's called normalization of deviance in the safety industry.
The two CCR divers who got killed deep inside the system a few months ago were different. They made a decision that proved much more dangerous than expected and then couldn't catch a break, but they had the gear, training and experience to go where they went and fully understood how serious a dive that was.