Well, ya know, a lot of times an old folk song needs to be added to in order to become a pop hit. Somebody may need to add a bridge, an intro, parts for backup singers, or an orchestra part.

(Come to think of it, when I am forced to listen to pop tunes in the supermarket, the 'orchestra part', which has been reduced to a ditty played on a synthesizer, is often the only part worth hearing.)

Anyhow, if somebody adds that stuff, s/he deserves credit for writing it.