You have a limited exposuer to "POP." Much of my material is 50 years old, even more is 100 to 150 years, and some is 200. They have commercial/pop composers/performers like Cole Porter, Steven Foster, Joe Young, Richard Rodgers, Jimmie Rodgers, Charlie Parker, Johnny Mercers, Jerome Kern, Oscar Hammerstein, Lorenz Hart, Benny Goodman, Ira Gershwin, Ray Henderson, Gerorge Gershwin, Lew Brown, Duke Ellington, Ray Charles, Count Basie, Fats Waller, Tommy Dorsey, Oscar Peterson, Ella Fitzgerald, Bobby Holiday, Miles Peterson, Miles Davis, Stan Getz, Nat King Cole, Louie Armstrong, John Coltrane, Count Basie....and outside of Foster this is not even the civil-war-era...and beyond.

The list for 1970 to present could be equally as long (Doors, Who, Animals, Turtles, Jimmy Dean, Jagger, Plant etc)....but it is a shorter time span.

You are painting apples and oranges with a mighty broad brush. It is a stupid question. You might as well ask, "Why do uncommon surnames like Gershwin and Rodgers appear more than once?"

Your view is probably skewed because all you know and play is "Folk" and you seldom step outside your "comfort zone."

Sincerely,
Gargoyle