Ok there's all the signalling between states that breaking a cable has. That also works for false flag operations, or true flag operations while making it look like a false flag operation (etc).

But also, cutting these cables doesn't stop communications. There are other land and undersea routes, and maybe terrestrial radio/satellite routes as well. You might damage these cables so that communications travel other routes which are more observable (or less observable). Or you might damage these cables so you can modify them elsewhere to enhance observability before they're repaired (or as part of the repair process).

Or it could be a training mission for your elite squad of cable biting sharks.

Lots of potential for intrigue here.