Isaiah 48:9

"For my name's sake will I defer mine anger, and for my praise will I refrain for thee, that I cut thee not off. Behold, I have refined thee, but not as silver; I have chosen thee in the furnace of affliction. For mine own sake, for mine own sake, will I do it; for how should my name be profaned? and my glory will I not give to another."

Right here is God's answer as to "Why?" he had refrained from destroying a reprobate and sinful nation who fully deserved such a destruction, no less than it had been deserved by Sodom and Gomorrah. Dummelow pointed out that God's refinement of Israel was unlike the refinement of silver, that is, the removal of all the dross, "would have meant the destruction of Israel."[9] There is no question whatever as to whether or not Israel deserved total destruction, because their wickedness even exceeded that of Sodom and Gomorrah, as Ezekiel reported in Ezekiel 16. Why, then did God not do it? The abbreviated answer is that to have done so would have endangered, or perhaps destroyed, God's plan of human redemption. God had promised that through the patriarchs Messiah would be born, through whom all the families of the earth were to be blessed; very well, the destruction of Israel would have checkmated the achievement of the birth of Messiah through the posterity of Abraham, or at least rendered it impossible to be proved or documented. Therefore, "for the sake of God's promises," he was stuck with Israel until the Eternal purpose had been realized.

Note the question here, "How should my name be profaned?" the argument here is exactly the same as that of Moses is Numbers 14:13ff, to the effect that if God should execute upon Israel the destruction they deserved, the pagans would declare that it was because God was unable to save them from destruction; and the pagans would have heralded Israel's destruction as a victory of their idols over Jehovah! Moses' argument prevailed with God at that time; and this passage shows that the argument was still valid in the times of Isaiah. Lowth gave the meaning of Isaiah 48:11 thus: "God would not destroy Israel, that he may not be blasphemed."[10]