Even though the land was under Israelite control, seven tribes hadn’t occupied their lands. Part of the reason was that they had no allocation; part of the reason was that they hadn’t asked for an allocation. Joshua challenged them on this point:
Joshua 18:3How long are you going to wait before taking possession of the remaining land the Lord, the God of your ancestors, has given to you?
Three men from each of the seven tribes went out and mapped the remaining land, which was then allocated by lot.
They didn’t manage to drive out the Canaanites from all of it, and they even had to battle iron chariots for part of the land, but they had officially taken possession of the land.