Lots of reasons already given and I think they are valid. Cost would have been a big reason too. Back then, and up until the advent of plastic pistols, semi-auto pistols were more expensive than revolvers. In the 1950's, the M1911-A1 was still the standard sidearm for the U.S. military and they were not being sold off as surplus. Back then, if you wanted a 1911, the sole source was Colt and Colt was still busy making replacement slides for the military.
Yes and no.
The US military wasn't surplussing 1911s in the 50s, 60s and 70s but it wasn't hard to find a surplus 1911 in very good to excellent condition at a really good price.
That was one of Colt's major post war challenges. Colt produced about 629,000 1911A1s during the WWII. Those pistols along with over 1.27 million made by other government contractors including Remington-Rand (about 878,000), Ithaca (about 340,000), Union Switch and Signal (about 55,000), and Singer (500) resulted in 1.9 million 1911A1s produced. Despite the US military not officially surplussing them until now, enough 1911s came home with returning service men that the civilian market was awash in them through the 50s and 60s and they were still common in the 1970s. Colt sold very few commercial 1911s after the war and due to the numbers of 1911s and 1911A1s on hand no new 1911A1s were purchased by the government during the Korean war. Colt was in dire financial straights and was sold to the Penn-Texas Corporation in 1955.
Adding to Colt's sales problems and also contributing to the continued popularity of the revolver in law enforcement were the Colt Commando (49,000 delivered to the US government) and S&W Victory Model revolvers (over 570,000) made during WWII. Many states had received revolvers for national guard units during the war and many of those states then surplussed those revolvers to police departments at no cost, creating more pressure for local departments to standardize on a revolver, rather than a pistol.
Another factor was that the 1911 had a reputation (unwarranted in my opinion) of being difficult to shoot compared to a 4" or 6" .38 Special revolver. From a training perspective, the .38 Special DA revolver was seen as a better choice.
Adding to the picture, while the Victory model remained in limited service in the US military until 1969, surplus revolvers were also common on the used market in the 50s, 60s, and 70s. These also included the re-chambered .38 Special Victory models, some very nicely done, that were re-imported from commonwealth countries that had acquired them through lend-lease, These revolver further flooded the used market, suppressed prices for used commercial revolvers, and competed with new revolver sales.
One thing most shooters today are not aware of is that the US gun manufacturers of the era were some of the most biggest supporters of the Gun Control Act of 1968. The import restrictions and point systems for pistols and revolvers passed to reduce the number of "saturday night specials" were all about limiting importation of less expensive new and surplus handguns, in order to increase sales for US made handguns. It had almost nothing to do with actual crime prevention. We got thrown under the gun control bus by our own firearms industry.
But I digress... You have to also remember that many police departments, in particular smaller departments, did not purchase service handguns under contract and issue them to officers. That's a modern construct that has arisen out of political and civil suit considerations. Prior to those issues arising it was common for officers working in small police departments to acquire their own revolver or pistol, usually from a list of suitable models, and/or with inspection and approval of the police department's armorer or contracted gunsmith. Some departments provided an allowance to purchase a handgun, others did not. Even in departments where service handguns were issued, there was often an approved list for privately owned handguns. Officers back then were more likely to have prior experience and preferences in handguns, and the environment was much less litigious.
For an underpaid police officer that didn't work for a large department that issued service revolvers, a used revolver in very good to excellent condition was preferable to a new revolver. When I started in 1985 - late in the revolver era - the department's officers purchased their own .357 Magnum revolvers and as a result carried a variety of .357 Magnum revolvers including the Ruger Security and Police Service Six, Colt Trooper and Lawman, and various S&W K, L and N frame revolvers chambered in .357 Magnum. I purchased a used Service Six, primarily because it was in excellent condition, had a good reputation, and was significantly less expensive than the available Colt or S&W options at the time. I'd have carried my personal 1911 in a heartbeat, if they'd have let me.
