It doesn't have to be this way though. Instead of having, say, quotas on how many speeders they need to catch in a given month, maybe they could use that time proactively helping people or something. I guess that is too utopian.
If you don't catch speeders, you up the risk of speeders causing a vehicular crash, which can lead to injury or death for you and me. Legislative branches passed laws around maximum vehicle speed, cops enforce that as a deterrent. It's for all of us, not the waste of time you seem to be suggesting?
I was in Texas recently and saw first hand what it looks like when police enforce 0 traffic laws. It ain't pretty.