Although the greatsword of Sigma is already pierced through the forehead of the Diamond Golem, that doesn't mean it was already over. The core is still intact and even if the Diamond Golem already stopped moving, that doesn't mean the golem will no longer move. As long as the core is still intact, it has a possibility to stand up again and fight.
The other girls decided to take this chance to seal its movements in case the removal of the core took a while and the golem revives. That way, they can take down the golem again in case it happened again. As for the guys, they climb up the golem and helped Sigma extract the core out of the forehead of the golem.
Due to the main reason that the golem is made from diamond, it took too long but the core is still intact that which made everyone extracting it frustrated.
"The extraction is not getting anywhere. As expected of diamonds, it is not easy," Bladeheart's father sighed.
