I mean, you aren't wrong. Cronkite was a celebrity. However, he was specifically selected because at that time he was more than a celebrity. Cronkite was a journalist who was universally trusted and beloved. Cronkite was the voice of the 20th Century. His coverage of JFK's assassination and, later, the moon landing are still watched by students and anyone interested in the impact of the media on society. When Cronkite said something, you believed it. When he retired from CBS, the whole country was saddened. Anyone who only knows about television news from our modern clusterfrack may have a hard time comprehending the importance of people like Cronkite and David Brinkley and how trusted they were because of their journalistic standards.
Cronkite was the perfect choice for a trip through the evolution of communication and its importance as a force for societal change. He could have said, "In 1723, cheese was accepted as currency by all major banks, second only in value to earthworms," and everyone in America would say, "Sounds screwy, but if Cronkite said it, it must be true."