Personally I do it because it's the closest I will ever get to feeling like a space explorer. You are neutrally buoyant (weightless) completely relying on your equipment for survival and able to see places IN the earth very few people will ever experience, plus I love a challenge. When most people think of cave diving they imagine really small holes and limited visibility. Sure, that can be it if you want or you can visit places like this,
https://youtu.be/TTICP6m-FyY?t=594
^ THAT is why I do it. Also I spent about 2 years in initial training and continue to train every time I dive. Our goal is to drive the risk to 0 which isn't reality but I feel less safe driving to some of the caves than I do diving them.