Why are names important to Piggy?

Jack does not reveal Piggy's name to the rest of the boys. During the first meeting Jack tells Piggy to, "shut up Fatty." To which Ralph replies, "His name isn't Fatty it's Piggy." Until that point Ralph was the only one who knew Piggy's nickname as Piggy had earlier told him, "I don't mind what they call me as long as it isn't what the boys called me at school...Piggy."