It's true that a lot of people are dismissive of anything that's not absolutely mainstream, and populist comedians feed into that. However, I'm still a little bit surprised to see this thread for 3 reasons
a) I haven't see any specific examples of comedians mocking folk

b) Some comedians are quite into folk. Stewart Lee, for example, is a big fan of (some) folk music. I'm sure I've seen him on TV talking about Martin or Eliza Carthy, he chose Nic Jones' Penguin Eggs as one of his favourite albums in an interview, and he played an acoustic version of "Galway Girl" (almost folk?) in one of his shows.

c) some comedians were folk musicians. Billy Conolly being a pretty famous example...