If I can throw out an analysis from my view, I blame ruger.
A DA revolver is more complex than a SA, and when you could buy a top quality ruger SA for less than a DA smith or colt, there was little encouragement to go the DA route. People in the 70s were still enamored of cowboys, and all through the 60s and 70s, people had chances to buy small and large bore cowboy reproductions by every **** company in europe. They had top quality repros brought in by interarms. They still had opportunities to buy other SA models, but the driving leader was the ruger SA model.
In the mean time, unless you were looking at the model 29, there was a dearth of top quality big bore DA models. Dan wesson wasn't a big player. The Colt .44 magnum, the super redhawk, they came out in the 80's IIRC, and were rather limited in availability for a while.
So, in my experience, until the mid 80s, you just weren't capable of getting the large bore DA. Prices were at a premium, and availability stunk.
During the 80s, lets face it, we were a more prosperous country, and a more prosperous group. We started spending. The silhouette shooters and hunters brought DA revolvers into greater availability. Gangster/pimp types started buying BIG DA revolvers, as a showy piece. (who can ever forget the scene in "Get Shorty? It did reflect reality.)
Since the 90s it does seem that there have been level sales, but the DA is still far behind the SA in popularity. I still hold the same two things accountable. Cowboys, and price of the product.
My observations.