Because they will be beaten, imprisoned or killed if they disobey. Tyrants have efficient methods to make people behave. If someone commits a crime in this country, we try to make the punishment fit the crime, but in countries like China, the punishments far surpass the crimes and I bet the court system is a hoot too. I know sometime it really stinks in this country because humans make errors, and some are just mean, but it's not a policy like it is in China. In Singapore, a fairly decent country, folks get caned for chewing gum. Gum is illegal there.