As one of the mainly missing club audience I would make a couple of points.

When I started attending clubs they started early evening, 7.30ish. This has now pushed back and back so there's less music in the evening and fewer chances for newbies and less variety. At the other end of the night more and more of the audience seem to be leaving early during the guest's last set leaving, in some cases, only half the number that started the evening. Doesn't make for a great atmosphere.

There is also (I think) more participation in making music than back in the seventies and eighties. People are attending sessions and if they're there then they're not in clubs.

There is an audience for folk music but it is finding venues other than clubs to hear it in and a new wave of performer is coming along who is meeting that need without playing the clubs.

Steve