Some songs are promoted commercially so well that everyone knows them. They are not
really folk songs because they are manufactured for the market. That doesn't mean they're not good, it just means that they are intended differently.

A folk song reflects the tradition of a specific community that is not part of the commercial music industry. It is generated from families in a specific (usually isolated) locale and
many of the voices are not trained but retain the musical nuances of the folk style they represent ie: Southern US mountain, field hollers, rural blues, Southern chain gang,
early spirituals, certain songs from Ireland, and the other British Isles, (not usually done by professional entertainers or performers), the same applies to all over the world.

As they say in politics, follow the money. In folk music, follow the tradition.

Frank