Some commentators claim this is the case because it is known that Cyrus allowed the worship of different idols to continue. But the text does not say that it was Cyrus who broke the idols. Instead, God is the subject of the sentence, and it is a reference to spiritual victory; the evil that opposed the kingdom of God would be completely destroyed.
9 And behold, here come riders, horsemen in pairs!” And he answered, “Fallen, fallen is Babylon; and all the carved images of her gods he has shattered to the ground.”