That's why it existed in the first place. I didn't ask that. I asked why God didn't destroy it. This you have not answered, nor, I suspect, can you. After all, if God was in the business of destroying everything associated with Himself that would be used as an idol if not destroyed (which is the principle you appealed to for why the SoT can't really be associated with Christ), the brazen serpent would certainly have been destroyed. It was not.
Well, it certainly was, and for the reasons I said:
(2 Ki 18:3 KJV) And he did that which was right in the sight of the LORD, according to all that David his father did.
(2 Ki 18:4 KJV) He removed the high places, and brake the images, and cut down the groves, and brake in pieces the brazen serpent that Moses had made: for unto those days the children of Israel did burn incense to it: and he called it Nehushtan.
Once again, you erred because you dont know your Bible.