Before Richard Digance, the show was hosted by Jim Causley (who made a much better job of it, IMO). His farewell message on web said,
"There were several issues that contributed to my decision to leave the show, not all of which i shall discuss here but to be as politely vague as possible; uncompromising situations made it impossible for me to do otherwise. I was hugely saddened to leave BBC Radio Devon as making a folk radio show focussing on traditional Devonshire music has long been a dream of mine."
So we really have little to go on as to why both presenters have left and (more importantly) why there is no replacement for the folk show.

Marje