Very intersting thread but, as usual, it seems to have been hijacked onto other agendas.
Anyway, as to the original question 'why prof folksingers quit?'
I have just taken a look at my 'Folk Directory 1970' and there is listed about 350 folk clubs nationwide. There are only 230 odd acts listed. If this is a representative sample it seems it needs about one and a half clubs to support one folk act. If the clubs decrease (and we know they have-read other threads) the demend for folk acts also decreases. I think it is called supply and demand.
Why did I quit? No demand in the first place!