Why did the fig tree decline to be king?
Bereishis Rabsi (20:15) The fig tree represents Devorah. She did not want to abandon her Torah, or her prophecy.
Malbim: Even a person like this (he is not spiritual, but he is powerful and can provide them with comforts) has a semblance of perfection that is pleasant to himself. He does not want to abandon it for the sake of the nation.
What is "Maski"?
Sha'arei David: Why didn't Rashi say honey of the fruit itself? (Midrashim discuss fig honey, e.g. Tanchuma Tetzaveh 10.) It is difficult to say that it is because the fig tree hints to Devorah, i.e. bee. Perhaps it is because she taught Yisrael, even though she herself is exempt from Talmud Torah, like bees' honey, which is not from the bee itself. The Zayis and vine allude to Osni'el and Gid'on, who taught Torah, that they themselves are commanded about; oil and wine come from the fruit itself.
Malbim: It did not mention benefit to Hashem and people, for it gives no real benefit, merely what is pleasant.
