The final days of the Kingdom of Judah are deeply tied to the personal tragedy of its last ruler, King Zedekiah. Unlike the kings who came before him, his downfall was not caused by idol worship or deep moral corruption. Instead, it stemmed from a specific failure in leadership and faith when presented with clear prophetic guidance.
The primary approach among commentators is that the evil the king committed was his refusal to listen and yield to the explicit warnings of the prophet Jeremiah. Jeremiah begged the king to surrender to the Babylonians in order to save the city. However, Zedekiah refused, driven by his fear of how the Jewish people would react [רש״י, רלב״ג]. This specific failure sets Zedekiah apart from his predecessors. While former rulers like Jehoiakim committed terrible acts, Zedekiah avoided those sins completely. His wrongdoing was limited entirely to rejecting the prophet's guidance and breaking the oath he had sworn to Nebuchadnezzar, the king of Babylon [רש״י, מלבי״ם].
Although the king's personal failure was highly specific, it merged with the broader wickedness of his generation. The entire nation constantly ignored the warnings of the prophets who were sent to them daily. This stubbornness pushed them to a point of divine anger that could no longer be healed, as they absolutely refused to repent [מלבי״ם]. Furthermore, Jeremiah was not sharing his own personal thoughts or ideas; he was delivering a direct message from God. Despite knowing that these warnings came directly from Him, the king still chose to reject the guidance [מצודת דוד, ביאור שטיינזלץ].