Because the Lord humbled Judah because of Ahaz, the king of Judah, since he completely apostatized (ἀπέστη ἀποστάσει) from the Lord.In his afflictions he continued to apostatized against the Lord (2 Chronicles 28:22). In the next chapter, it refers back to
all the implements which Ahaz the king polluted in his reign and in his apostasy (2 Chronicles 29:19)The Septuagint is translating a different term as apostasy in this passage.The Hebrew term is ma`al, which means to act unfaithfully or to act treacherously. Thus Ahaz, even though he is the king, is a traitor to his God and acting treacherously against God. The temple implements were given by the funds of individuals and dedicated to the Lord for holy purposes. Ahaz, however, decided to put them to purposes other than those originally intended by those who donated them. He also abandoned the worship of the Lord to attempt to curry favor with other worldly powers (2 Chronicles 28:22-25). As a result, the Lord delivered him to his enemies.
It took a different king, Hezekiah, to set things right again and to rededicate the offerings back to their original purpose. Apostasy requires a restoration.