Few believe that reason of sending them behind bars was: Ancestators of Kauravas wanted to conquer Gandhar state and hence put the king and all sons behind bars after victory.
Shakuni’s dice were made from his father’s bone as asked by his father to him. Thus dice always obeyed and showed what Shakuni would ask for. Some believe dice were of ivory and Shakuni was expert in creating illusion and thus created illusion of required numbers on dice.
Because we see good even in bad, Shakuni has a temple in his name in Kerala.