And also like in any workplace, if the management thinks you're not of much value to remain, they'll get rid of you and save themselves some money, and in the case of Vidal, make a lot of money out of it as well.
Don't get me wrong, Vidal must stay, he's the best in the world when in form box-to-box and one of my favourite Juve players. His positive attitude alone makes him extremely valuable, but if he keeps lacking in performances, the management would be tempted.