Rabbi Lazer Ginzburg seems to say the greatest thing a Jewish leader can do when his people are causing Gds anger, is to say to Hashem: "It's because of me that the yidden are sinning!" (he supports this idea). With this idea by the sin of the golden calf, why didn't Moshe accurately take the blame for the sin and say to Hashem: "It's because of my delay in coming to them that they made the golden calf"..? This seems to be the greatest response Moshe could have said and he didn't. Why not?
That which is properly called accurate is true, and that which is true is accurate: it is never a righteous thing to lie to God—true humility does not involve or consist in pious lying, but rather the virtue of humility consists in the ability acknolwedge the truth about oneself, regardless of how little or big it makes you feel or look: this is real humility. Therefore, Moses who "was more humble than any man on earth" (Bemidbar 12:3), would never lie in order to seem what he was not.
Moses, who was as outraged at the infidelity of Israel as God Himself, could not 'admit' what was not true, namely, that he was himself at fault somehow, since Aaron his brother was the leader of the people while Moses was gone: Moses could not at once attend the people and God. If not so much as a goat was allowed to set foot on the mountain, how is Moses who dictate to those at the bottom? He cannot.
Shmot 32:15 And Moses returned from the mount, carrying the two tables of the testimony in his hand, written on both sides, and made by the work of God: the writing also of God was graven in the tables. And Joshua hearing the noise of the people shouting, said to Moses: The noise of battle is heard in the camp. But he answered: It is not the cry of men encouraging to fight, nor the shout of men compelling to flee: but I hear the voice of singers. And when he came nigh to the camp, he saw the calf, and the dances: and being very angry, he threw the tables out of his hand, and broke them at the foot of the mount: and laying hold of the calf which they had made, he burnt it, and beat it to powder, which he strowed into water, and gave thereof to the children of Israel to drink. And he said to Aaron: What has this people done to thee, that thou shouldst bring upon them a most heinous sin? And he answered him: Let not my lord be offended: for thou knowest this people, that they are prone to evil.
As we can read, Moses and Aaron were both against the idolatry; Aaron was weak and gave into what he ought not to have as a Mosaic leader, and Moses' successor, but Moses was fully against and in no way responsible for what they who were at the bottom of the mount did while he waited at the top for God to write the law on the tablets of stone, and blamed Aaron for his inexcusable indolence or cowardice in the face of apostasy from the only true and living God.