All the estimates of the number of folk clubs up to about 1963 or 4 are low. From 1964/5, the numbers grew quickly and massively. By the mid 70s, Perform (remember that?) was lamenting the state of clubs, and by the time of the recession of the early 80s and the folk scene reached a bit of a low, folk clubs seemed to be losing popularity.
In other words, the heyday period for folk clubs was quite short really.
Where I live, in south Cheshire, we had a folk club in Crewe with a mixed approach .. trad, blues, contemporary ... and an intermittant club in nearby Nantwich, and then (still running) a club in Sandbach - these 2 towns are about 5 miles from crewe in opposite directions. Now there is just one club in Sandbach which does not have the range of music (mainly contemporary and blues) and does not have anything like the audiences that the Crewe club had in its heyday (but at least it is still operating every week!). In contrast to the heyday years, there are now music (with some song) sessions every night of the week in the surrounding area.
When the Crewe club had a reunion a few years ago, it had considerable difficulty finding a pub room to use .... fifty quid rental for a night compared with one pound when we ran the club.

In conclusion?
then heyday of clubs was short lived.
It was generational.
there are fewer suitable pub rooms around now.
people's tastes are more sophisticated and they require better surroundings for their leisure than a dusty upstairs pub room.
There are a lot of informal sessions that reach out to the ordinary pub goer, but they tend to be participative rather than for a passive audience.
There are arts centre/theatre venues that programme folk music (but not in Crewe!).
There is a gap in the middle - something reasonably accessible, local that would hook people into a wider interest in folk music.

Or I could just be reflecting a local situation, instead of national trends....

Derek