Additional.
Partly it's because I wanted to make the sort of game, I wanted to play. Where my choices did matter, and where there were things beneath the surface. Where what the NPCs did and why they did it had as much meaning for them as my own actions did for me.
Obviously, I'm limited to a degree by my coding, but I still wanted it to hang together. I wanted it feel real. Yes, you as the player know what you want to achieve, and I'll try to give you as many ways possible for you to achieve it. But I also wanted the NPCs to want to achieve things to. Sometimes that may work with your agenda, sometimes against it. But no one said life was easy...