From the examples you give of the groups you like, Dazbo, I think it may well be the material that is the reason. Then again.... I recall the first time I heard a "folkie" sing "Rose of Allendale" (Mary Black had just recorded it) and I wondered, "What's the difference between this song and the many hundreds of similar songs from the 19th Century that are not as well received by "folkie" audiences? Familiarity? A well-known singer recording it?"
It's an ok question, I reckon. More to it than first meets the eye.
                               Joy