Opportunities don't appear in a vacuum.
These aren't two random dudes who BMW (and Harley) decided to drop a whole bunch of cash for them to go on a motorcycle adventure. Obviously they had enough cachet (or least Ewan does) that these companies saw a quid pro quo in having them represent their brand.
It's easy to say, "yeah, if I had the cash", but they don't acknowledge that these guys worked to get to a point where they were marketable enough.
Better to say, "yeah, I just need to go to acting school, do bit parts in commercials and theater, be an extra on low budget movies, go to countless auditions and battle tens of thousands of other Hollywood Hopefuls, to finally land a juicy role and be noticed by the industry. Then I can capitalize on this fame and leverage my contacts in the film industry to build an Adventure Travel entertainment brand from scratch".
But no, people think it's as easy as, "just give me the money and I would totally do that ride."