Humans have poor understanding of emotional rules. Probably every poster on here has experienced greatly misreading another individual emotionally. Further, people often don't act emotionally how they would expect themselves to act, for example we have all experienced frustration at someone else's irrational concerns and yet we are all guilty of holding irrational concerns of our own. This is the crux of why hard-coded emotional rules do not work - we do not have an understanding of what emotional 'rules' make someone feel real.
By moving towards autonomous state-based actors we move away from this issue. The actor's state transitions will of course be defined rules (hard-coded or learnt) but by abstracting the actor's emotional state from the specific context (e.g. specific actions trigger emotional state transitions which trigger responses, instead of a direct response to a specific action), the programmer prevents them-self from projecting their own beliefs/emotions/logic onto the actor.
Further, autonomous actors are more extendable. Consider an autonomous actor that is hard-coded to move towards 'upset' and 'angry' emotional states when experiencing 'pain'. Simply by associating a new world action with 'pain', one can trigger an emotional response from an autonomous actor that has not experienced that action before. When working in hard-coded emotional rules, this would not be possible.