If we're talking about areas which have a lot of venues to hear public performance of folk music, I'd suggest that you need two things: people who are prepared to put the time and effort (either professionally or as a volunteer) into organizing; and audience members who are willing to spend their money on folk music in order to make it financially viable. If either of these elements is lacking, you won't have a vibrant public-performance folk scene. However, it's possible to have a vigorous grassroots folk community without having a lot of performance venues (although admittedly it can be good for the grassroots scene if people are able to be enthused by getting to hear good performers from time to time).