I think the reason will come down to technology. If it was just to get away from Angrif Djun- that wouldn't make sense. With the palace, they can relocate to any continent they want- well past the point where he could follow them. I think they are going to realize that humans will inevitably spread everywhere- and that they will have technologies like guns that will make them incredibly dangerous in a whole new way. And Cutter will freak out about leaving when he realizes this.