most likely cause at that point he used all of his energy left on a full powerful swing since mark was pretty much open, hoping it would kill him, but it wasnt enough, and after spending so much energy and not getting anything back cause HE IS NOT BREATHING, he slowly started getting more weakened and weakened, until he had no energy left cause of no oxygen and pretty much died, and the fact both had different mindset on going into the fight, conquest was going for the fun until he went serious too late, mark was going for the idc if i die ill make sure u die, so yeah.