What makes folk music accessible is its ability to reach people because somehow they've heard it before. This could also be said for popular music but in the folk traditions, they are generally a cultural phenomenon and not manufactured for a market.
Folk music regardless of where it emanates has to have an element of being derivative
of some other form of music not attached to the associated culture.
This would be true of Australian music or any other national form.
Chords characterize a style of music. The selection of chords determine this.
Mainly, chords in folk music reflect European-based derivatives. The reason is that
Europe really employed more sophisticated harmonic structural values rather than rhythmic or microtonal scales as found in other less Europeanized music.
Even the highly isolated or regionalized music of for example, the Appalachians contain elements of Europeanized music and even the African-American blues and offshoots from this are derived from hymns, marching bands, classical piano compositions (employed by Scott Joplin or Jelly Roll Morton) however there may be some notable exceptions to this by early forms of field hollers and quills and mouthbow or early banjo playing that come from African musical forms. But the 12 bar blues owes its form to conventional chord progressions even though the melodies deviate from standard European forms.