The only difference between a staff post and a contributor is that one line by their name. If Forbes didn't want me to associate their name with the content they would have distinguished it better.
Same problem with TED's TEDx conferences. Why do so many brands want to throw away their cachet by stamping their name on random contributors' content?
Because some distributed content generation platforms like YouTube, the Huffington Post, Bleacher Report, and others have proved to be enormously successful and popular, so other content companies have tried to emulate that success?