I can't really remember what it was like way back when, I think maybe there was a kick against pasteurised beer, juke boxes.....piped music! and plastic pubs. Maybe the folk club format was of it's time like the hoover gave way to the Dyson, still do the hoovering though! For me it works for all the reasons GSS said but they are just one of a plethora of ways to enjoy the music genre, at the session in the Tap & Spile in York we gather to enjoy ourselves and have a night out with music and we do reach a lot of people who would not normally attend a folk club but have since listening and joining in at the tap. Maybe it is worth exploring whether the clubs that struggle are the ones who lean heavily towards traditional music and the ones that survive are the ones that have a more eclectic mix of performers. I do not really have sufficient knowledge to give a scholarly opinion but I am interested to know.