I think there’s an intangible reason why Casey Kasem achieved the success he did, and the parallel I see is with Johnny Carson.
Both Carson and Kasem had a “format.” Johnny had his monologue and interviews, Casey played songs and told stories.
Both Carson and Kasem stuck to their plan. Johnny didn’t do movies, Casey’s attempt at “TV Top 40” was brief.
Both Carson and Kasem were originals. Johnny wasn’t like Jack Paar, Casey sounded nothing like Wolfman Jack, “Cousin Brucie” or Alan Freed.
Both Carson and Kasem ignored copycats, and there were many. Johnny had Merv Griffin, Joey Bishop and Joan Rivers. I doubt you remember the radio countdown shows from Scott Shannon, Dick Clark or Shadoe Stevens.
The “X Factor,” I think, was a comfort these performers offered. A Tonight Show guest once told Carson that no matter where they were, at the end of the day they would turn on the TV and spend time with Johnny. A kid moving to a new town needed time to make new friends, but could find Casey Kasem on the radio right away.