[ghock]

"But really, at the end of the day, they did this because it was a rush"

Diving isn't really compatible with "a rush", especially not cave or other technical diving. You have to be focused, methodical and patient. It's more meditative than anything, you can't even breath too quickly without risk. While still having to keep track of a lot of things. In "rush" type of activities it's the sensation of almost losing control that is fulfilling, while in technical activities like this it's rather the sensation of being in control.