One thing that weighed into Jobs recommending Cook was that it was Cook that built up the operational foundation that helped Apple grow after Jobs returned from exodus.

Apple's success post-Jobs return wasn't just down to product and design, it was about turning those into a business that could scale. And that was what Cook did. So Jobs rightly got credit for direction, strategy and focus, but these all count for less if you can't execute. And that was what Cook did for Jobs. Jobs was the ideas man, but Cook helped make them work.