[jtriangle]

If you're doing tethered ROV stuff, the weight of the teather is a big big deal, so adding 4 additional wires is a non starter. For the stuff that goes extremely deep, they use fiber because it's much lighter. It presents significant cost increases of course, which, you'd want to avoid if you can.

[teruakohatu]

You can get neutrally buoyant cables:

https://bluerobotics.com/store/cables-connectors/cables/fath...

[sgtnoodle]

It's still mass, drag and cost.