It's worth mentioning that cable breakages happen quite often; globally about 200 times per year [1] and the article itself mentions that just last year, two other cables and a gas pipeline were taken out by an anchor. The Gulf of Finland is evidently quite shallow. From what I understand, cable repair ships are likely to use ROVs for parts of repair jobs but only when the water is shallow so hopefully they can figure out whether the damage looks like sabotage before they sever the cable to repair it. Of course, if you're a bad actor and want plausible deniability, maybe you'd make it look like anchor damage or, deliberately drag an anchor right over the cables.
Cable repairs are certainly annoying and for the operator of the cable, expensive. However, they are usually repaired relatively quickly. I'd be more worried if many more cables were severed at the same time. If you're only going to break one or two a year, you might as well not bother.
1: https://www.theverge.com/c/24070570/internet-cables-undersea...
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