Judges 3:4

Not. Various reasons are assigned, on the part of God, for not exterminating these nations at once. But their being spared so long, must be imputed to the disobedience of the Israelites, otherwise they would surely never have been tolerated with their idol-worship in the land of promise, to contaminate, by their wicked example, the manners of God's people. If they would have redeemed their lives, they must at least have given up the land and their idols. As the Israelites proved so little zealous in destroying the latter, they were justly punished by God, in being deprived of what would have contributed to make them richer and more comfortable in this world. (Haydock)