God brings the new covenant because there is something wrong with the first one:

Hebrews 8:7-9

For if there had been nothing wrong with that first covenant, no place would have been sought for another. But God found fault with the people and said: "The time is coming, declares the Lord, when I will make a new covenant with the house of Israel and with the house of Judah. It will not be like the covenant I made with their forefathers when I took them by the hand to lead them out of Egypt, because they did not remain faithful to my covenant, and I turned away from them, declares the Lord.