Why do tortoises dig?

To dig a hole in soft sandy ground for their eggs to be stored in until they hatch. The tortoise buries their eggs and then leaves them. The mother tortoise will never have anything to do with her eggs after she's deposits them in the ground and buries them. The eggs are buried and are safe from egg eating predators and warm until they hatch. Then the young turtles have to dig their way out of the sandy ground, and get into the water, before they are eaten by predators.