[btoptical]

It's easier to lay a subsea cable than to go overland in remote areas. Take a look at the subsea map of Africa as an example. In Africa the subsea links are there because it's too remote to run cables through the jungle or across the Sahara. Additionally terrestrial cables are more frequently cut than subsea cables. In India terrestrial fibers are cut routinely every day to the point that they have to allocate extra repair margin for the links.