Livestock working in a factory contribute to the production. These animal-people work selflessly for 24 hours a day. Because of the structure of their bodies, they belong to the robots who get hungry easily. As long as they continue to work, energy pipelines on their seats continuasly replenish their bodies with the necessary energy. Therefore, they obediently sit in their seats throughout their lives. Once they leave their seats, their life is over. Robots, who are imprisoned for their whole life, can not be given an electronic high intelligence. If they had the ability to make decisions, it would be very hard to control them.
On the other hand, for robots who have no lofty aspirations in life, this actually is not a bad thing. After all, they can have a nice chat, they can continually live in this environment, and they do not need to worry about the shortage of food and an idle lazy life. They are happy to be captives. It looks that being in prison is easier than living in freedom.