Logically all kinds of people move on to all kinds of other opportunities for all kinds of reasons. All kinds of things happen.Are you really that gullible? I'm sure you also believe Tim Cook word for word when he says that Apple products are, in fact, magic and not just advanced technology.
There's a difference between saying someone is straight up lying vs. honoring an NDA. Apple is notorious for over the top NDAs. Anyone who leaves Apple who is higher up in the company has never said anything bad about the company within several years of leaving. That speaks volumes. Forstall was practically forced out the door and you never hear a peep. Same with John Browett. But sure, be gullible and believe everything the millionaires and corporate shills tell you and take it 100% at face value. Just search Google for the stories over the years that creep up from sources talking about how things really go down inside Apple. It never matches the narrative that they feed you! And Apple isn't unique. This happens at a lot of companies. It's all about PR spin and having everyone come out looking good. In reality, if everyone was super happy then there wouldn't be these huge names leaving. Just sit and think about it logically.