[jemmyw]

The problem with seeing it as a test of response is that the test changes future responses. Where previously it might have been possible to do a surprise attack on cables, govts will now (hopefully) be looking at ships maneuvering near by with more suspicion.

[jiggawatts]

The problem is that in some areas there are both cables and ships in such a high concentration that it's impossible to police.

Generally undersea cables "land" at major port cities because that's where it is convenient and also that's where the data centres are.