It's easy to forget (or not know) the history of Top 40 radio. Considering what Top 40 radio, nay, the entire Broadcast Radio business has BECOME one could be forgiven for, to use the term, "not giving a shit." BUT as it turns out Top 40 radio was a thing that happened, and the emergence of Top 40 radio as a distinct business practice coincided with the recording of the first rock and roll records. That's not suggesting that Top 40 created Rock and Roll, only that Rock and Roll was literally the first thing to "happen" to Top 40 radio itself.
The Top 40 radio format was created by a guy, Todd Storz, the program director at KOWH in Omaha Nebraska. He did it in 1951 and the practice spread.
The anecdote they tell about his "Eureka" moment is retold ably in James Miller's colorful Flowers in the Dustbin: The Rise of Rock and Roll 1947-1977,
"One night, Storz suggested to Stewart that the repair to a local watering hole to conduct some marketing research. As they drank, they listened to what the clientele wanted to hear on the jukebox. And they listened, Storz was struck, again, by a paradox.
While in the army during the war, he had noticed that soliders took pleasure in hearing exactly the same songs played over and over again. In the bear he noticed the same thing" "The customers would throw their nickels into the jukebox and come up repeatedly with the same tune. Let's say it was "The Music Goes Round and Round." Even more striking was the reaction of the bar's waitress. After almost all the patrons had left, with her pick of songs to play, "what number would she select? Something she hadn't heard all day? No-- invariably she'd pick 'the Music Goes Round and Round."
Storz had a bright idea, "Why not play records on their radio station the same way that patrons were playing them on the jukebox- over and over again?"
THEY WANTED HITS. PEOPLE WANT TO HEAR HITS. Also, they liked faster music- if you look up that Music Goes Round and Round track- which I think I've blogged prior, you'll see that it is an uptempo song- present at the very creation of Top 40 radio.