So, is there a reason for there being no police on the streets at all? The only times I've run into police outside of missions is when I pull out a gun in public and a civilian calls 911 (which they don't do that often), I don't interrupt the call (which I pretty much always do) and can't evade the ctOS circles (it's pretty easy evading the ctOS circles). And when they do show up, you can still very easily just evade them and they despawn when they've lost you.
I'm just racing down the streets like a madman knocking over lantern posts and smashing through fences and wrecking public property and the police just don't care. A massive crash due to a traffic light malfunction? Police don't care. A bunch of gang members driving around town in a mad chase after you, shooting up and crashing into everything? Police don't care. Crimes noticed by ctOS? Police don't care. Blow up some civilians with IEDs? Police don't care.
Use your weapon to scare of a criminal and save someone, then non-lethally take down the criminal? A civilian called 911 and now the police are hunting you down with lethal force.