>>18096229 (OP)
because the Canaanites were wicked people that worshipped abominable idols in complete impunity for 700 years. God not only establishes a home for the Israelites but make them an instrument of Divine Vengeance.
Also, hyperboles. Many time, the narration in Joshua uses words like "utterly destroyed" when talking about cities and armies. I think we would both agree that armies are relatively fair game - especially since in all of those cases, the Canaanites were the attacking party - but then we get to the cities, right? Except when we return to the same "utterly destroyed" city five chapters later, Canaanites still live there. (See Joshua 10 vs Joshua 15), possibly because they killed everyone *in* it at the moment of storming it, but allowed some form of surrender to take place beforehand, allowing those who wished to be captives to do so.