The reason why it is ok to eat burgers, hot dogs, and pizza with your hands but not rice is bc rice gets everywhere. If it were a rice ball, eg onigiri, ppl would accept this behaviour. It is all about mess control. Sushi is originally supposed to be eaten w hands but became chopsticks bc ppl insisted on having the wasabi and soy sauce separate from the fish+rice and dipping it into sauce with your bare hands would be messy.