The reason why most slave were denied to read was because most slave owners believed that teaching such skills was useless, if not dangerous. They assumed that slaves had no use for reading in their daily lives, and that literacy would make them more difficult to control, and more likely to run away. In this case slaves were get smarter and run away or obtain knowledge and use it against then. There was the fear of an educated black man. Ideas are a powerful thing and it would make them feel inferior to slaves.
Deserts are characteristically deserted and lack an abundance of water, so this dry climate provides a fitting geographic theme for a group of people that learn to survive with a limited water supply.
