Why did Israel fail to destroy the Canaanites?
Israel failed to destroy the Canaanites because they became soft-hearted, thinking they could use them as servants and left off destroying them. This disobedience, contrary to God's instruction, allowed the Canaanites to influence Israel, taking them into idolatry, just as God had promised would happen.
Les explains that during the period of the Judges, Israel occupied the land of Canaan but did not destroy the Canaanite people as God had instructed. They got soft-hearted, thought they could use these people for servants, and for one reason or another left off destroying them. As God had promised, the Canaanites then influenced the children of Israel and took them right into idolatry. Les notes this is hard to comprehend, since Israel had the manifestation of the miracle-working power of Jehovah God in their midst, yet turned to pagan idols. Their history throughout the 300-400 years of Judges was a roller coaster, reaching spiritual heights under good judges, who were merely rulers under God in a God-centered government, then falling.