Why would God drive out Canaan's nations only little by little, according to Deuteronomy 7:22?

Answer: Wild animals would multiply

"You will not be enabled to eliminate them all at once, or the wild animals would multiply around you" (Deuteronomy 7:22).

“The LORD your God will drive out these nations before you little by little. You will not be enabled to eliminate them all at once, or the wild animals would multiply around you.”— Deuteronomy 7:22 (BSB)