The said "pocket battleship" weighted 53,500 tons and was the third heaviest ship afloat at the time. Her sister perished after a prolonged battle involving half the British home fleet, sunk one of the Royal navies' most famed warships and severely damaged another new battleship. After that battle, she was hit by aircraft and ship borne torpedoes and two other battleships practically expanded their magazines in order sink her.
Tirptiz was a valuable target, which merited the risky assault. South Korean corvette was not. That's before we consider such an attack is rather difficult (i.e. impossible) on a ship that is underway ...
McHrozni
Just as an aside, I know one of the chaps on the mini subs. Yes, really. He's still alive. Absolutely fascinating chap. Mr. Lorimer.