Police departments always go with the best equipment they can afford, and this includes everything from police cars to sidearms. Following the police car analogy, if the department buys Fords, then they train the motor pool to work on Fords, and the spare parts in the shop are for, yup, Fords. Over time Ford, because of training and support, becomes the norm for the department. The same is true with handguns.
When I went thru the academy in 1976 I was one of 7,200 deputies employed by the county who were trained on the .38 caliber S&W Model 10, the work-horse of law enforcement sidearms. The county issued our ammo, and required us to qualify quarterly. That meant that at any given moment there were over a quarter of a million rounds being carried by deputies, and that many more being used in qualifying every 90 days; all in, the county probably went through 1.5 - 2 million rounds of .38 Special each year. In terms of economy of scale, there was no reason to swap from the .38 Special to a more potent round as the costs would have been prohibitive.
