I know this post is satire but if I had to say it's because Exo's were perhaps created to look up towards humanity. Not be us, be our technical better. The technology used to create Exo's is said to be extremely advanced, and it's also said that only the Ghosts of the Traveler are able to decipher their technological wonderment. Sorry about nerding out there. *Ahem* Well the demand is high for robotic companionship in reality, perhaps the creaters of the Exo's were a bit more dirty than we know, hm?