The death of a great leader often leaves a deep spiritual void. With the passing of Gideon, the Israelites reach a tragic turning point and quickly abandon their faith. This immediate regression into idol worship is not a sudden anomaly but part of a familiar historical cycle. The nation habitually returns to its destructive ways the moment the judge who guided them dies [מלבי״ם]. Following Gideon's death, the people fully embrace idolatry once again, allowing the worship of Baal to reclaim its central place in their society [ביאור שטיינזלץ]. The primary approach among commentators is that they select a specific idol, Baal-berith, to crown as their new deity.
This spiritual betrayal directly explains the nation's severe lack of gratitude toward Gideon's family after he is gone. During his lifetime, Gideon earned the name Jerubbaal because of his fierce war against and deep hatred for idol worship. Once the Israelites return to the very practices he fought to destroy, they naturally turn their backs on his household, making it impossible for them to show any kindness or respect to his remaining legacy [חומת אנך].