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?

The ship was sailing from Russia and the captain is Russian. Using a Chinese ship is a good trick from Putin.

As for the core of your question: there is no benefit, it's just his mentality. "The West" supports Ukraine so let's just do some harm, retaliate in some way. Burn some buildings here and there, plants some inflammable materials on airplanes etc. Pointless for you and me, meaningful for that guy.

Does "Chinese ship" really mean anything here? As far as I understand the ship official registration is a very vague concept https://en.wikipedia.org/wiki/Flag_of_convenience