I recall the late, great Col Jeff Cooper refered to the M14 single action as an "affectation". He also called the LAPD changeover to double-action only revolvers as an engineering solution to a problem that was better solved with proper training and discipline.
This is purely conjecture, but I would think that removal of the DA feature was a move on the part of S&W to take the M14 out of the serious police and self-defense category and place it squarely in the sporting use and competition category of firearms. After all, a sporting competition instrument could not possibly be used for homicidal purposes, right??