Yi Peng 3 crossed both cables C-Lion 1 and BSC at times matching when they broke

October 2023 there was similar incident where Chinese cargo ship cut Balticonnector cable and EE-S1 cable. Chip named 'Newnew Polar Bear' under Chinese flag and Chinese company Hainan Xin Xin Yang Shipping Co, Ltd. (aka Torgmoll) with CEO named Yelena V. Maksimova, drags anchor in the seabed cutting cables. Chinese investigation claims storm was the reason, but there was no storm, just normal windy autumn weather. The ship just lowered one anchor and dragged it with engines running long time across the seabed until the anchor broke.

These things happen sometimes, ship anchors sometimes damage cables, but not this often and without serious problems in the ship. Russians are attempting plausible deniability.

What are some concrete reasons why someone would want to damage these cables? Who benefits?

Assuming it was intentional, just trying the waters. Testing what the response is, who actually responds versus who's willing to sweep the incident under the carpet, how hard any response is and how quickly it happens, how much of the internet infrastructure is affected for how long, etc... etc... that's a lot of useful information as preparation for an actual attack.

That's very similar to how the "accidental" flights over neighbouring territory works as far as I understand. This happens regularly between many countries. Just far enough to get some response, but not enough to get shot down immediately.