What did he not know?
Rashi: [Yaravam ben Yo'ash] did not put to his heart that Malchei Aram consumed them in the days of [his grandfather] Yehoachaz ? "Ki Lo Hish'ir li'Yhoachaz? va'Ysimem ke'Afar Ladush" (Melachim II, 13:7). Even so Yaravam did not retract from his father's evil.
Radak: He did not know that it was due to his sin; he did not repent from his evil.
Malbim: That foreigners ate his strength. This explains the Mashal ? fire burned the bottom of the cake, which was not flipped. So Melech Ashur consume [Efrayim's] strength, took their money and exiled them.
What is the meaning of "Gam Seivah Zarkah Bo"?
Rashi citing Targum Yonasan: Also weakness came to them, and they do not look.
Radak: [Normally] a person repents from his evil way in his old age, for he sees that his strength ceased and he is going [to die] like all people. The great length of the afflictions was like old age. Also at the end, in the days of Pekach and Hoshe'a ben Elah, they were like an old man, and still they did not repent. Zarkah is Po'el Omed (the action applies only to the subject), as if it says Nizrekah.
Radak citing Ibn Ezra: Nature brought old age upon him.
Malbim: Just like the top of the cake [that was not flipped] is not baked and is soft, [Efrayim] became like an old, soft (weak) man.
