There's a very old thread on why police agencies went to DAO.
To recap, DAO was developed at the behest of LE trainers. Recall that back in the '70s and '80s, most agencies issued revolvers and officers were trained to fire DAO. It was believed that manually cocking a firearm would either lead to unintentional discharges or would get the officer killed (DA is faster). Now, fast forward to the '90s when everybody is going to pistols. The first batch of pistols were either single action 1911s or Browning HP; neither of which were really accepted by agencies because of their single action only feature. The second batch heralded the era of the Wondernines (S&W, Sig, Beretta, etc) which featured a DA/SA trigger.
Well, a lot of cops couldn't handle the transition from DA first shot to SA single shot. Training time and budgets would permit proper training and some cops just couldn't adapt. As a resolution, may instructors asked the manufacturers to build a DAO pistol which would make it easier for revovler trained cops to transition to a pistol. It worked. Scores actually increased.
Civilians don't need DAO because, being civilians, generally will take greater time and interest to master their guns than the average cop (who sees it as a tool of the trade). Not to knock cops and there are some great shots out there (Pride, Cirillo, etc) but this is my observation from years of being in the trade (yes, I'm revolver trained).
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