The big change happened in the 1970s, when using the excuse of some police assassinations, the federal government encouraged police nationwide to discontinue using “Old West rules”, and adopt “SWAT rules”.
This means things like, assume ambush at traffic stops, brandish gun frequently, it is essential to assert control in all situations ASAP, etc. The end result is more cops getting killed, often with their own guns.
Taking the paramilitary nonsense out of our police forces would go a long ways towards restoring the respect that they once enjoyed.