Wildlife, not wildfire!

Things like a whale getting entangled in it, and then using all its strength to get free, breaking the cable.

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.

Think of shark biting at cable, etc. Remember these cables just sit on top of the ocean floor.

Do you know how thick these submarine cables are?

Most importantly, once a shark gnaws at the cable, various waterproofing and weatherproofing layers get broken, and seawater goes deep inside the cable, then corrosion happens, breaking things further...

The cable is absurdly thick and absurdly armored only in shallow waters near the landing point (ie. where it is expected to be affected by stuff like boat anchors). In open ocean the cable is actually surprisingly thin for how robust it is.

there are videos out there, sharks like to bite those cables