I don't see how a whale would get caught in a cable that's laying on the ocean floor. They don't float.

When the cable goes over mountain ranges and cliffs and valleys on the ocean floor, it can end up thousands of feet from the bottom sometimes.

You appear to just be making stuff up.

Submarine cable is buried when it's at depths of 2000 Meters or less. It is done so using jet-plow technology. Beyond depths of 2000 meters the cable simply sinks to floor and rests there. It most certainly does not hang across a valley the way high tension power lines do above ground. Also cable routes are carefully planned to avoid trenches wherever possible. Where that's not possible it's simply sunk by its' own weight down to the ocean floor.