Probably because the player, generally being more aggressive than the AI on their side, puts themselves in a more exposed/flanking position, which is going to make the AI target their ship.
Most of the time, the AI's choice of target is based on relative ship locations. Say there's a clump of ships and a single ship facing them. The single ship will pick a target such that strafing around it will put all the other ships in the clump behind that target. So if the ships are in a line, for example, the ships on the ends meet this criteria. If the ships are in a triangle, any of the ships does (and there's some logic to figure out which one is preferable when there are multiple options). If the ship is being flanked, it'll try to pivot around one of the flankers.
Another way to think about it is the ship trying to maneuver in a way that puts enemy ships in each other's way, by picking the "best" enemy ship to pivot around to achieve this. This is good defensively (for obvious reasons), and is also good offensively since it leads to flanking.
("Best" iirc has to do with how far around it needs to pivot, plus some other considerations...)