Apple has made cook a billionaire. The appropriate salary for him is $1. The appropriate additional capital grant is $0. He's a major shareholder, he has wealth at risk both up and down with his and the fate of the company.
If he thinks they can't replace him and go as well he has financial incentive to stay. If he thinks they can replace him and go better he only has financial incentive to stay if they pay him ever more every year.
This way of thinking is a great way to ruin a company. After that every employee will think about whether Apple will give them just the minimum so that they don't leave for another company.
2 billion dollars worth of ownership of the company is the minimum? Come on! Every single individual employee will be fired if it is in Apple's financial interest. If Apple have a large number of employees better off somewhere else they have a very, very big problem. It should be stinkingly obvious the rules of the game a quite different when you own 2 billion worth of stock compared to when you're using your paycheck to pay the rent and pay down your debt.
If he thinks they can't replace him and go as well he has financial incentive to stay. If he thinks they can replace him and go better he only has financial incentive to stay if they pay him ever more every year.