I can't really comment on how things are in the U.S., but the U.K. folk scene certainly isn't dominated by professionals, more's the pity. - I'd say the majority of performing participants lose money by doing so, and that includes the lower end of those who actually get paid. There is open access to a significant proportion of gatherings, but because (in part) of the lack of professional quality they tend not to attract many new faces. Besides which, if you give something away for free, most people will think it is worthless.