Ever since Hagoromo's passing, all that Kurama ever received from the humans was betrayal and fraud. Again and again, humans used him to fulfill their desires and still treated him like nothing more than a mere weapon. This anger inside Kurama kept piling up until all that remained was hate and disgust for humankind. And to put fuel to the fire, Madara came and forced Kurama to bend to his will. Luckily, as time went on, Naruto managed to calm down that anger bit by bit, until finally, Kurama could trust again.