Assuming this was orchestrated by a nation state I wonder what the goal is? Just causing mayhem and incurring cost? Is there some specific function of these cables? Is this a negotiating tactic?
If you have a plan to sever every major fibre link into and out of some country then the only way to rest the effectiveness of your plan is to sever just a couple and see what happens.
The Cold War equivalent is to fly up to the border and see how the enemy fighters intercept your bombers.
Alternately it’s “making a concrete statement” in response to a thinly veiled threat.
E.g.: if a western government threatens to cut Russia off from the Internet they can cut a fibre to two to make a point that the west is just as vulnerable.
Generally undersea cables "land" at major port cities because that's where it is convenient and also that's where the data centres are.