Perhaps Brown was not the easiest director to deal with for busy actors who worked elsewhere, like my favorite Lloyd Bochner, and perhaps some found out radio just wasn't their cup of tea. After all they could make much better money elsewhere. The repetition of actors also suggests a kind of closed shop where you had to be good buddies with the others or you wouldn't be cast. I would like to have heard more of Theodore Bikel, Bochner and others instead of Fred Gwynne so often myself.