It also sends two messages: "We can do this to any of your cables", and "we're willing to" – with an implied "we could easily do it to all of them at the same time".

And the last scenario is the real problem: While there are enough cable repair ships to continuously handle a normal rate of simultaneous peak failures, fixing multiple cuts can quickly exceed their capacity. (There's nothing that says an attacker can only cut the same cable in one spot!)