I'm less concerned about denial of service via cutting cables, and more concerned about the tapping of cables for wholesale data snarfing.
The USA were caught tapping cables in the cold war https://en.wikipedia.org/wiki/Operation_Ivy_Bells
Now this doesn't mean that the Russians are right now tapping these cables; they could be simply mapping their precise location etc for later or using them as a training exercise.
The Russians have submarines for this kind of thing, and I bet they're regretting they sent a surface ship. See a list of some of the submarines used for tapping cables at the bottom of the Yandar article.
This is like killing a person with polonium, which is made in just a handful of facilities around the world. Russia wants to cause worry. They want "respect", which mainly means fear.