How come? I think it'd be likely that there will eventually be a hybrid text-to-speech engine that is trained on the narrator, and can continue where they left off.
I haven't listened to the audio yet (can't do it right now), but I guess professional voice workers for non-fiction texts tend to use a neutral, maybe slightly robotic voice because that's the industry standard. It's similar with news announcers on TV or on the radio. The professionalism removes the human element.