The a-capella singing on the radio usually isn't traditional music (folk or otherwise). It also depends on why I'm listening. Some music is more demanding to listening to and I don't always feel like it. I'm not knocking unaccompanied singing; it's just not a style of music I usually like very much, so if I just want to be entertained or am listening with half an ear, I will probably switch it off.

I did switch someone off only the other day. I could happily do without long, drawn-out, overly-emotional, unaccompanied renditions of "Amazingrace" forever. Other people might love them; that's what makes ball games.

Actually, I do sometimes like a-capella singing with multiple parts, which has become popular again. I never much cared for choral music, but I always liked some, like Guilliaume Dufay. Now I've started to like more of it. Tastes change with time. It would be boring if they didn't.