Albert Barnes Commentary Joshua 18:3

"And Joshua said unto the children of Israel, How long are ye slack to go in to possess the land, which Jehovah, the God of your fathers, hath given you?" — Joshua 18:3 (ASV)

This backwardness probably arose from the people's unwillingness to abandon the nomadic life in which they had been born and raised, and to settle in permanent homes, and perhaps also from a dislike of the exterminating warfare that came with completely dispossessing the Canaanites.