This has not always been the case in the past.
I remember having a conversation with Derek Brimstone years ago and he went on an on about how he would not book Martin C, because he drew his own audience who did not return to see other acts that Derek had booked.
So an example of a contemporary folk performer excluding a revivalist tradtional singer despite the fact that singer Martin filled hos club.
However I ran a club [despite the fact that i sing mainly traditional songs] that booked derek brimstone martin c, ewan macoll peggy seeger cyril tawney peter bond nic jones johnny handle richard digance. a mixture of trad contemporary, and i made it viable.
I know who had it right and who was inclusive