Why does Arthur call off the siege of Benwick and return to England?

Arthur calls off the siege of Benwick and returns to England primarily due to the growing internal conflicts and the need to address the instability within his own kingdom. He recognizes that the ongoing strife threatens the unity of his realm more than the conquest of Benwick. Additionally, his commitment to his ideals of chivalry and loyalty compels him to prioritize the well-being of his people and the integrity of his rule over military ambitions.