Their singing tradition wa reasonably intact in July in 1973 and they were still active in making songs
We didn't go back till 18 months late to find that had stopped completely; everybody had a portable television they had been ably to buy in Woolworth's
Presumably the advent of mass produced 12 volt TVs came at a price that was attractive to many!

From this the next logical question has to be:
If the tradition stopped in the mid 70s, has it hit a brick wall and become a fossilized genre, or has it transmuted and is in fact alive and well.
Cheap cassette players also became widely available at this same time (70s). This would have been another nail in the tradition's coffin.
Consumer electronics exploded in the 70s with the Japanese leading the onslaught.(sony and akai to name but two) This put means of recording and transmittal within the reach of everyone.
There has been much emphasis on what folk was then but continual argument as to what it is now, in terms of it's creation and continuation.
I hate to say it but you have danced around a response to this question Jim (and I do not say this provocatively - Both I, and I suspect many others, would be interested to hear your views on this)