God promises David that his kingdom will endure forever, then why did Israel's throne become empty for nearly 600 years before Jesus?

Some relevant texts: 2 Samuel 7:12-16 , 2 Chronicles 13:5 , Psalm 89:20-37 , 1 Kings 11:36 , etc. It seems that God promises David a *continuous* Davidic line on the throne, without interruption (especially the text in Jeremiah 33:17 ). But this didn't happen because before Jesus' birth, the Davidic line was interrupted with Zedekiah, leaving a near 600-year gap between Zedekiah and Jesus unexplained. How should we interpret God's promise then?