in the book thief why does hans get sent home

Hans gets sent home after breaking his leg in an accident.

"The olive green truck was on its way toward the camp, maybe ten miles away. Brunnenweg was telling a joke about a French waitress when the left front wheel was punctured and the driver lost control. The vehicle rolled many times and the men swore as they tumbled with the air, the light, the trash, and the tobacco. Outside, the blue sky changed from ceiling to floor as they clambered for something to hold."