Because God of his own mere grace undertook their protection, as he promised to do, and disappointed the hopes and design of their enemies; of which see on Isa 7.
Related Commentaries of 2 Kings 16:5
2 Kings 16:5
5 Then Rezin king of Syria and Pekah son of Remaliah king of Israel came up to Jerusalem to war: and they besieged Ahaz, but could not overcome him.