Prior to my Army career, I was on a Texas Gulf Coast city PD for a short time (1965). They required us to use a 4" barrelled revolver in .38 Special. You could carry the (gasp, shudder, too powerful) .357 if you wished, but were limited to .38 Sp rounds in the cylinder.
We were issued the 130-grain FMJ round...PC has been around a long time...most everyone replaced them with heavier handloads in the .38 Sp case once shift inspection was over.
As I've said before, most departments today have done away with height/weight standards to increase "diversity", and most cops don't put in enough time on the range to become really proficient, so you're left with the need for a low-recoil, hi-cap "spray&pray", relatively fool-proof, pistol. Add into that equation the increasing CYA PC attitude of the administration, and this is what you get. Then, after something like the North Hollywood shootout they come back to their senses for a while.