Re: Why does the fiddle often play only the verse, not the turn?
I think there's a more simple evidence proved explanation :
Acordion players are sober over-trained super-healthy athletes who can play all night long without suffering tendinitis or muscle pain, so they play both A & B parts even the D or the Y-Z part.
At the opposite, fiddle players are brittle drinkers, so if one turn they go to the bar , next turn they go to the toilets. CQFD.
Re: Why does the fiddle often play only the verse, not the turn?
I think Cajun music has become way too regimented. My opinion only, but the accordion player should play what he wants, then pass to someone, and that person should play what they want and how long. Marc Savoy and Michael Doucet do this.