The destruction of the silk worm was a priority. As the Iraq weapon had been upgraded as later examination of captured weapons showed . This gave the weapon a require capability so if weapon had been successfully decoyed by the battleship it would have reacquired a target. So the weapon posed a major threat to ships in the vicinity.
Caribbean wrote:"Eyewitnesses aboard both the battleship and USS Jarrett recall the missile veering sharply northwards seconds before its destruction, presumably distracted by the battleship’s chaff or jammers. However the tactical track aboard HMS Gloucester showed it ignoring the chaff and maintaining a steady course to the end"
The missile sharp turn would be it clearing to acquire a new target. Thankfully the sea dart removed the threat.