Because it was Gods plan:
Ps. 90:1-3. "Lord, You have been our dwelling place in all generations. Before the mountains were brought forth, or ever You have formed the earth or the world, even from everlasting to everlasting, You are God. You (God) turn man to destruction; and say return you children of men.
ISA 63:17 O LORD, why hast thou made us to err from thy ways, and hardened our heart from thy fear? Return for thy servants' sake, the tribes of thine inheritance.
Jeremiah 18:1 The word which came to Jeremiah from the LORD, saying: 2 Arise and go down to the potters house, and there I will cause you to hear My words. 3 Then I went down to the potters house, and there he was, making something at the wheel. 4 And the vessel that he made of clay was marred in the hand of the potter; so he made it again into another vessel, as it seemed good to the potter to make.
5 Then the word of the LORD came to me, saying: 6 O house of Israel, can I not do with you as this potter? says the LORD. Look, as the clay is in the potters hand, so are you in My hand, O house of Israel! 7 The instant I speak concerning a nation and concerning a kingdom, to pluck up, to pull down, and to destroy it, 8 if that nation against whom I have spoken turns from its evil, I will relent of the disaster that I thought to bring upon it. 9 And the instant I speak concerning a nation and concerning a kingdom, to build and to plant it, 10 if it does evil in My sight so that it does not obey My voice, then I will relent concerning the good with which I said I would benefit it.
11 Now therefore, speak to the men of Judah and to the inhabitants of Jerusalem, saying, Thus says the LORD: Behold, I am fashioning a disaster and devising a plan against you. Return now every one from his evil way, and make your ways and your doings good.
12 And they said, That is hopeless! So we will walk according to our own plans, and we will every one obey the dictates of his evil heart.
13 Therefore thus says the LORD: