"in singarounds I hear a lot of songs (by people like MacColl, Tawney, Dave Goulder, Sydney Carter, Martin Graebe and Graeme Miles) which are recognisably new songs in a traditional idiom."
that is because in a melodic sense they are restricted to a few modes, it is a genre which is going to go nowhere, it is limited musically, it refuses to take on influences from other traditions[how many songs are written using the hijaz scale, for example].
Dave Goulder is the one person who has experimented with using a different mode for a song [the walrus and the carpenter]
"very few contemporary songs have the story-telling structure which is so characteristic of trad songs"
an over simplification there are plenty of tradtional songs, there are plenty of trad songs that have little story structure, martin said to his man [a very old tradtional song] ,greensleeves, the water is wide. benjamin bowmaneer,the cadgwith anthem holmfirth anthem
FURTHERMORE some contemporary songs have a story telling structure,. the Black Fox,1649,Sreets of london.