Let's think about the appeal of the two musics:

Bluegrass (in my view, at least) has two areas it focuses on:
It's a vocal/harmonic style, but the sung words are really not too important; the singing becomes just some of the music.
and
It's an instrumental/harmonic style which depends heavily on speed, instrumental virtuosity, and a certain kind of insistent rhythm.

Maybe there's a third aspect, too: The subject matter of the singing seems rather circumscribed. Themes that spring immediately to mind are old-fashioned Christian religion, and mother, and then a few others like trucks. But, as I observed above, the subject matter isn't as important as the musical style; the words are sort of a necessary evil.

In folk song, the appeal (at least to me) resides mainly in the words; the instrumental accompaniment, if any, is sort of a condiment to serve with the main meal of word meaning.

Folk music people are likely listeners who primarily enjoy the story or word stream.   Bluegrass people will be those who tend to focus on that hard driving rhythm and the characteristic harmonies found in bluegrass. As I see it, of course.

Now I know before I ever click the "submit" button that many here will see me as mistaken in this, if not wrong-headed, but that's my take on it.

Any comments? ("Come on, Dave! You know there will be comments!")

Dave Oesterreich