Original: This may have started because many prominent broadcast personalities – such as Walter Cronkite, Johnny Carson, David Letterman, Tom Brokaw, John Madden, Rush Limbaugh and Casey Kasem – came from this region and so created this perception.
Simplified: This may have started because many television show hosts — such as Walter Cronkite, Johnny Carson, David Letterman, Tom Brokaw and Casey Kasem — came from this area.