Maybe because cops are some of the lousiest shooters out there!!! Trust me I know first hand with 20 years experience as a master LEO firearms instructor. They just don't like to take the time to practice!!! In my department we classify j-frames as back up / off duty weapons. I designed a 50 round course of fire to include the 3,5,7 and 15 yd firing lines, to include a reload at the 15 yd line. the course includes 2,3 and 5 round courses of fire. This takes in consideration of the five round cylinder wheel guns.
Another problem I had as chief firearms instructor at my department was money. The sheriff didn't have the extra money to give me for ammo for practice periods for the deputies. That is a shame, even though we don't have a Dodge City jurisdiction! Practice, practice and more practice makes for best results after a gun fight!!!