How much is it DAs vs cops just not wanting to do their job to prove what they said would happen is true?

Cops don’t always arrest based on the law, but what they feel like doing. See Oregon where they decided not to police proud boy protests and tend to arrest anti-white supremacist type protestors much more.

How much is it the cops found they can prove their own point? If I make a bet that I’ll get last in a race, I’ll run slower. If one claims some policy will slow them down and They don’t actually have an incentive to win, Then there’s a chance they’ll slow down to be right so people will do what They say in the future.

What incentive do cops have to arrest or charge theft when cops keep saying it’s CA laws that are causing thefts to rise? They can make themselves seem right by not arresting people.