My last post was sent having not refreshed the thread,so others had already given some of the info I gave in my last thread.
As a past festival organiser, of course we want people to patronise the concerts, but recognise that there are also plenty of folk who come just for the sessions and not for the concerts, and pretty well most of these festivals named have a strong session element. They still bring money into the town and local businesses, if not to the festival itself. (Don't mention "economic impact assessments"!)
At the festival I used to help organise, we were able to get a local Council licence for can collections for donations from those attending "free" events, which all helps to keep the festival going.
"No such thing as a free lunch"!