For those who are interested on knowing why Tatooine is a desert planet and about the origins of the Jawas and the Tusken Raiders here it is :
Tatooine was once a lush world covered with oceans and with jungles and filled with very diverse and rich life. The domiant species of the planet was a very advanced humanoid race called the Kumungah who had created a planetary civilization and developped space travel long before the humans and most other species.
Against the wishes of the elders who wanted to focus on their homeworld the Kumungah decided to colonize other planets and as such sent expeditions to other planets. Sadly for them it turns out that their elders' advices weren't wrong as these expansion effort drew the attention of the species that was dominating and opressing the galaxy, the Rakatas who proceed to conquer and enslave the Kumungah just like hundreds of other species.
However the Rakata Infinite Empire was about to decline due to internal civil wars and of a plague that had begun to ravage the Rakatas, a plague which could eventually cut the Rakatas from their connection to the force. The Kumungah seized the moment to rise in revolt and chase the Rakatas from Tatooine, something that would have been unimaginable decades or centuries before.
Unfortunately they had chosen the wrong moment to rebel as the Rakatas while weakened were still very powerful and technologically advanced, and in retaliation bombarded Tatooine, destroying the jungles and boiling the oceans until the world was covered with nothing but crystal.
A portion of the Kumungah had managed to escape extermination by hiding into deep caves inside their planet but once they returned to the surface they had mutated into two different species: the small Jawas and the tall Ghorfas. Eventually the crystals that were covering Tatooine crumbled and turned into sand creating the desert planet that everyone know.
In this now very harsh world the Jawas tried at first to coexist peacefully with their taller cousins but they were hunted down or enslaved for their efforts starting a long and bitter feud between the two races.
Things would change when humans and other aliens came to Tatooine millenias after the fall of the Infinite Empire and the rise of the Galactic Republic. Large corporations hoped to find on Tatooine precious minerals that they could mine and prosper and brought with them large numbers of colons who were hoping to find fortune here. But there was no rich ore on Tatooine and the corporations left Tatooine, abandonning the colons here who now had to live in this inhospitable planet with few to no hope of leaving due to their poverty.
The Ghorfas who were already struggling to find and survive with the rare ressources left on their world were enraged to see these outsiders arrive and take their lands and ressources and started the first raids in a very long series against the colons, who came to call them the Sand People or Tusken Raiders.
Meanwhile the Jawas found in this new situation an opportunity to find refuge from their violent cousins and started to specialize in finding, using and selling technology and droids. They started also to hide their face and use gems to cover their true eyes, explaining why they seem to have shiny red or yellow eyes.
Of course an abandonned planet where there is no law and where you can do anything without getting punished could only attract the criminals and outlaws of the galaxy, and soon Tatooine became a refuge for pirates, gangsters, smugglers, gamblers and every kind of criminals giving the planet its very bad reputation.