Trump is a scumbag and not extremely competent as a businessman. He is however very good at manipulating people and selling his brand. He could have five times as much money as he currently has if he stuck his money in an S&P500 index fund and did zero for the rest of his business career. So, from the "making maximum amount of money", not very competent. He wants to sell himself as a sharp businessman and personality, and does so very successfully even if it doesn't make him nearly as much money. Dude has more than enough to live on, and past a billion it's really just playing for ego anyways so it does actually make sense. Rather than donate his surplus to fight malaria or whatnot, he'd rather engage in ego pleasing business deals that make far less money than competent investments. Becoming President would fit with that. He wants ego gratification and attention more than money or power. It's not as insane as it seems. Even a couple hundred million in the bank could let you live like royalty, so this is essentially his hobby.
And he's good at his hobby. Look at the folks who support him. If they looked up his previous behavior and held him to it, they'd be screaming that he was a commie pinko socialist. They're not. That's pretty good evidence of how good he really is at selling himself. It's kinda amazing, but moreso a comment on the American people.