Why did the Prophet (peace be upon him) pardon the polytheists of Mecca and not kill them, even though the People of the Book are given the choice between jizya or fighting, and those other than them are compelled to embrace Islam or be fought?

The disagreement among scholars regarding which disbelievers are eligible to pay jizya has been mentioned previously. The Prophet's forgiveness of the people of Mecca after the conquest has no bearing on the jizya, because they embraced Islam. There was no fighting from the direction of Al-Zubayr, and the Prophet, peace and blessings be upon him, entered Mecca, and its people embraced Islam and pledged allegiance to him. As for forgiving them in terms of retaliation and recompensing them for their evil deeds, that was part of his noble character, peace and blessings be upon him, to pardon, forgive, and respond to evil with good.