I’ve had very limited experience of low/no visibility diving - it’s hard to overstate how incredibly difficult it is to accomplish anything. You can’t see anything, you can only hear your own loud disorienting breathing, you can’t feel gravity, your sense of time goes completely out of the window. It makes moving very short distances hilariously slow. You constantly have to keep yourself oriented in full 3D space. If I had dropped something 10 centimetres from my face, I may have never found it. Trying to map out alternate routes through kilometres of unknown cave system with incredible time pressure? It’s a miracle they found even one route.