Why are cops always fishing for things when we have plenty of real criminals on the streets?

Why don't they go after rapists and murderers instead of trying to jam up some guy for an expired drivers license or not using a turn signal. Or even people who haven't done anything wrong at all. I remember one time me and my buddy were fixing to pull out of a park after walking around for an hour and this cop came up with some elaborate bs lie about he had driven and out like 5 times and was wondering why we were sitting there. Total lie. Then he wanted to search the car.

Why are cops always fishing for things when we have plenty of real criminals on the streets?
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