Creative musicians in the Folk world do not put as much or hardly any energy into improvisation, compared to Jazz Musicians, Songwriters put their energy in to writing songs not improvisation, you are talking Boloney
audiences do want to know what they are going to get, they do not expect to go to a Folk Club and have a whole evening of Rock and Roll and they are the ones who pay the piper..
On the positive side Folk Clubs provide the opportunity for home made music.