"It's very common practice for people into singer-songwriter music to try to keep all other kinds of music out of their venue. The problem isn't exclusivity in verbal definition, it's exclusivity in actual practice, hidden behind the verbal screen of the word "folk". "

You need to get out more Jack, and ask more questions. Perhaps in your corner of the world it is common practice for singer-songwriters to keep other kinds out of their venue, but I do not see that here.   I will grant you that there are economic forces that factor into booking possibilities, but I do not see exclusion of traditional music in circles like you described. I do see more exlusivity among traditional artists and venues than I do the singer-songwriter genre - here in the northeast.

I really don't give a flying fuck if you wasted six hours of your life at a session that wasn't your cup of tea - and if you could not convince the others to explore traditional music, then either you did not speak up or they were too limited in range to explore.