I'm glad someone introduced Townes Van Zandt ('Pancho and Lefty') as I think some others of his qualify; 'Tecumseh Valley' particularly.
'1952 Vincent Black Lightning' has the obviously modern motorcycle motif but is classic ballad form, boy meets girl, love at first sight, he is a bad lot, dies young.
Some of Larry Kaplan's songs tell stories very well, too, though not all are as singable as 'Old Zeb' which has taken on a life of its own. 'Hard Way to Peacham' certainly comes to mind (young family lost in snowstorm in unsympathetic world).
I agree that a singable chorus helps a lot in the process of a song becoming 'folk'.