Why were God’s people so prone to sin?
The normal reasons apply: They gave no attention to God’s will; they were seduced by the materialism of the nations around them; they trusted more what they could see than a God they couldn’t. The list goes on.
But in Jeremiah 21, the Lord places at least part of the blame on the leadership of Judah. Zedekiah (chapter 21), Jehoahaz (called Shallum in chapter 22), Jehoiakim (also chapter 22) and all their minions are addressed and condemned because they have not been obedient to the Lord. As goes the leaders, so go their people.
Neither of the two choices the Lord sets before Jerusalem is desirable: Stay, fight, and die, or surrender to the enemy and live in exile. I am sure there were those in Jerusalem who, Rambo-like, would choose to fight and die gloriously, but it is not the choice God wants Judah to make. The arrival of the Babylonian army is at the direction of the Lord and because of the sin of Judah. To fight Babylon is to fight the Lord. Surrender to Babylon is the beginning of surrender to God and the beginning of hope for the future.
Sometimes the best choice is not the obvious one, but it is always in keeping with the will of God. Know the will, follow that will, and the decisions will still not always be easy, but they will be right.