The only land he didn't buy belonged to the priests because they had a food allowance provided to them by Pharaoh, so they didn't have to sell their land.
Pharaoh gave Joseph the name Zaphenath-paneah, and arranged for him to marry Asenath, the daughter of Potiphera, priest of On. This is how Joseph rose to power over the whole of Egypt.
So Joseph made it a law for Egypt which is still is in effect today that one-fifth of all produce from the land belongs to Pharaoh. Only the priests' land was exempt since it did not belong to Pharaoh.
Also be aware that all of the priests, Levites, singers, doorkeepers, Temple servants, or other workers of this Temple are exempt from paying any tax, tribute, or fees, and you are not authorized to charge them.
I also found out that the food allowances for the Levites were not being provided, so the Levites had gone back to take care of their fields, along with the singers who led the worship services.
Don't you know that those who work in temples receive their meals from temple offerings, and those who serve at the altar receive their portion of the sacrifice on the altar?