I don't know much about undersea cables (although it is a fascinating subject), but I imagine there's no need to tap a cable in the middle of the ocean. If instead you tap it a couple miles offshore (even tens of miles), suddenly have a lot less undersea fiber to run. And if multiple cables come ashore at the same place, you can probably disguise it as just another fiber.

Of course, this requires a friendly country at one end of the cable, but that's probably not too big a problem.