This seems to be the trend in England. Audiences are dwindling. Each club has its own little nucleus of elderly folk who try to attend regularly. But as these people die or become incapable of turning out, the club withers.
But in England, ask 'the man in the street' where you can go to hear a live traditional jazz band, and he would be unable to tell you. In fact, he might not even understand your question.
The music gets so little exposure in the most influential of the media.
When Christmas shopping, I visited the store that has the largest collection of CDs in Nottingham. It has a section labelled 'JAZZ'. But I couldn't find a single CD that could indisputably be described as 'traditional jazz'.
The last two generations have grown up on the disco music of recent decades and are unaware of much else. Making matters worse, music education in schools is very limited. It seems to me that it's only the privileged few who even learn to play an instrument.
Fortunately, we have twenty or so brilliant musicians in the United Kingdom who are under the age of forty and playing fine traditional jazz. But that's not many in a population of about 65,000,000. In general the future for traditional jazz in England is not looking good.