I think that in the case of the UK the fact that most folk clubs and festivals are run by "amateurs" might have a bearing on the attrition rate amongst full-time performers (Remember the heated debate about this in the Melody Maker folk column way back?).

If you are a performer trying to make a living on the folk club circuit you tend to expect the organizers to be equally "professional" in their approach to running events. However, if the club organizer has a 9 to 5 job, a house, a wife and two kids to look after, the folk club has to be a hobby. Albeit an important hobby.

This, I'd say, has always been the strength AND weakness of the folk scene.

Personally, I know a few performers wo have done quite well over the years (supporting a family, paying off a mortgage, etc) but the are in the minority. Like the man said - don't give up your day job.