Entertaiment is a great way to keep the brain active and realeasing seratonin and dopamine. Entertainment often hits on the themes of backstabbing, murders and other themes that the human mind was evolved to deeply react to, in order to survive and understand the social world. This is probably why so many of the familiar themes, images and structures in entertainment have had such longevity.
Merriam-Webster defines Entertaiment as:
From Middle English entretenement, from Old French entretenement; see entertain. Also derived from inter-, between; and tenere, from the Indo-European root ten, meaning to hold inside. Related words are entertainment, entrainment, and emulation.