I would not assume the intention is to intercept data. Assuming this is accurate, it could be tactical repositioning given recent events. Some seem to think that Trump might actually take action in North Korea. If he does, that's going to radically escalate tensions between the US and China/Russia - both of whom border North Korea, and are keen to see them remain a buffer between US military installations and their homeland. Imagine some bizarro parallel universe where Russia and China are actively suggesting plans to invade Mexico and already well established in Guatemala. If we enter into another cold war era, electronic warfare including threats on communication systems (including satellites) would likely be the new invisible 'front' as all developed nations have become heavily dependent on these systems which remain extremely vulnerable.
Not so simple at the bottom of the ocean and working with pressurized cables, besides the fact that the data will most likely be encrypted at the link level.
Does it really matter? Most of the important data is already encrypted (and even the unimportant stuff like youtube video streams are served over HTTPS, not even sure why).
The real problem is them cutting or blowing up these cables.