Maybe he never ran for public office because he was afraid he would lose. I have no idea if that's true -- but it's as sound an answer as what you posted.
How could being POTUS be a "step down" by your standards, if Michael Bloomberg -- who I believe is a lot wealthier than Donald Trump -- wasn't above serving for 12 years as the mayor of New York City?
You just love to argue. Even if it’s pointless, like this one.