I'm 30+ years out of the English folk scene, but as I remember it, it was very encouraging to new performers, and we sat through (and applauded) lots of less-than-perfect acts. Club organisers actually encouraged them, and some internationally known talents made the journey.
Compactness was also a factor. When I lived there I could, and sometimes did, visit 7 folk clubs a week, within 1hr driving distance, and 7 or 8 festivals a year. Nowadays I see advertised even more festivals than then.
The American performers that we saw then, and now, are slick and professional artists, who but from their musical preference could fit into any musical field. Only a few English performers could match them.
Is the American scene one in which perhaps a quarter of the audience in a club could and would get up and 'do a turn' if asked? I can't answer that, but I do know that I was encouraged in England, and have been a folkie ever since. Mouthy ever since, too.