In nearly every adaption of the Jungle Books Kaa the snake is evil and attempts to kill and eat Mowgli. Is there a specific reason for why directors/writers of the movies try to turn Kaa evil, in spite of Kaa is one of Mowgli's trusted friends and mentors as depicted in the books?
I struggle to understand it as there are already plenty of villains: Bandar-Log, Shere-Khan, villagers, hunters and the Dhole.