"exist for the pleasure of the participants" I should bloody well hope so. I would disagree with the use of "only". I know lots of people that enjoy listening to sessions as non-combatants, the idea that because the performers enjoy what they do this excludes an audiences enjoyment is silly.
There are lots of sessions here in the Manchester area that regularly pull in punters, and one of the contributory factors is that they are allowed to have a conversation whilst the music is playing and don't have to show inappropriate reverence for the performers.
Folk clubs are basically middle class ghettos, riddled with obsequious mard arses who'll sit through a bungled amateurish murder of a traditional Ballad and clap the louder for it at the end, in a futile attempt to cover up their imbursement.
This kind of masochism doesn't suite most people and so they stay away
What a surprise.

PP