It's easy to forget at times, but the core character holding this entire movie is the newsman named Thompson. He's the one who's sent out by his boss to collect the testimony of all the people who were closest to Charles Kane.
His mission is to find out what Charles Kane meant by his dying words, as his boss tells him, "Find out about the Rosebud! Get in touch with everybody that ever knew him, or knew him well."
We spend the rest of the movie following Thompson around, and we never get a perspective on anything he doesn't hear himself from someone who knew Kane.