Although I'd love to see Bill Gates or Tim Cook as president, the fact of the matter is, they're more powerful being outside the government than in it.
The president's power is limited to what Congress and the Courts will let you do.
Tim Cook can make Apple do pretty much whatever he wants as CEO. Bill Gates is independently wealthy and really can just do whatever he wants. If he wants to pay billions of dollars to develop vaccines to help Africans, he can do that - he has nobody to answer to.
Same deal with Elon Musk. If he wants to spend billions of dollars to send a rocket to Mars, nobody can tell him no.
The president can't send people to Mars just because he wants to, though. He has to explain how that's a good usage of tax money right now.