"how can some of Ewan MacColls songs have evolved into folk songs? "
They didn't, and Ewan was always insistent on this fact - his sings never became folk songs
A couple of them ended up sung in very fragmentary form by Travellers but, as the Travellers singing traditions took a nose-dive when they all go tportable televisions this didn't go anywhere and MacColl said it.
We recorded bits Freeborn man but not enough to show it had taken root
Like with the settled Irish music, there has been a considerable rise in interest in instrumental music within the Irish Travelling communities, but that's in its early stages
First Time was turned into a pop song, which was why it caught on, but that never became a folk song and never will - it was a love song written for Peggy while they were apart
Repetition is not tradition otherwise the national Anthem and The Birdie Song would be a folk-song
Jim