Bond, black mail, guilt leverage, desensitization....
There is numerous reasons they could do it. You pretty much own a MF'er if you manipulate them into going cannibal. That being the main one imo.

Of course this all speculation but given where we are discussing it makes sense to ponder it. Someone will inevitably propose the inverse and say it is a ghost story to scare ppl off and work as a kind of hazing.