Either,
1. Because the people had made Jehoiachin king without his consent. Or,
2. Because he had some notice, or at least a suspicion, of his intentions to rebel against him, and to join with Egypt against him, as Zedekiah his successor did. But whatsoever was the second and immediate cause of it, the chief cause was God's commandment, or the direction of his providence, as it was said, 2 Kings 24:3.