He wanted to go away last year, and it's no secret he was close to City.
Juventus convinced him to stay, but made a gentleman's agreement that they would not stand in the way of a sale the following year if he wanted to go.
Same scenario with Vidal. He was close to United, but stayed a year, and we sold him for peanuts. In the meantime, Vidal screwed up in terms of another incident with drinking and driving, which made it impossible for him to stay, due to our strict policy.
The rumors of City died last year, as soon as the first stories of Bonucci's son's ilness appeared. Much has not changed, he wanted to try something new last year and the same this year, where the situation and future in Juventus has probably become so unsustainable, due to various controversies, which made the final push towards an exit.
Due to his son's health, he is locked to an Italian club though.