"Why do folk clubs charge an entrance fee?"

Maybe to pay the rent, publicity, electricity, heating, cleaning, etc. Perhaps some make donations to charities or even give some money to the occasional performer. Sometimes I'd guess the people who run the club would like to eat and stuff like that.

Hell, we have people in Canada who bitch about paying school tax because they have no kids in school or road tax because they don't drive. But, as a society we do benefit from education and roads. Seems like a foolish question to me.