I would expect folk musicians in most countries to be "left-leaning"

In my opinion, performing traditional music is a conservative activity per se, and "in most countries" and ethnic contexts, it is firmly connected with the dominating forces. Only in societies where "folk music" is defined to be the music of a lower class that collectively struggles for more recognition, performing it may be viewed as a statement in favour of that struggle. The champions of that movement, such as Pete Seeger, are so well known worldwide that we may tend to overestimate their share in the whole scene. In the USA, you can of course simply call all non-leftist music "Country" etc.