Perhaps it’s a difference in communication experience, and effectiveness? Maybe the person who is already famous has lots of experience with talking to people and conveying information — perhaps they make more efficient use of a small amount of information — whereas the person with a lot of experience on the subject matter, but is poor at communication, is unable to effectively communicate the subject matter. One must be able to retain people’s attention to effectively communicate; this takes skill.
Perhaps it’s a difference in communication experience, and effectiveness? Maybe the person who is already famous has lots of experience with talking to people and conveying information — perhaps they make more efficient use of a small amount of information — whereas the person with a lot of experience on the subject matter, but is poor at communication, is unable to effectively communicate the subject matter. One must be able to retain people’s attention to effectively communicate; this takes skill.