Why is Rob Dyrdek worth a lot of money?

He has been a pro skateboarder since 1990ish. He has 14+ pairs of signature shoes for DC. Owns a clothing company called Rogue Status w/ Travis Barker from Blink 182. Sponserships from Alien Workshop, Silver trucks, Spy+ optics, and huge money from Monster energy drinks. Rob & Big and Fantasy Factory royalty checks for life.