So, how about an experiment? Considering the US has experimented with red light cameras with well below good results overall, from a safety claim. Speed is a significant safety issue (or at least the authorities and the insurance people keep saying and making the rules to enforce) but we also have guns. Lots of guns.
Take almost an exact duplicate of the standard / common residential speed camera, drop a few of them in rural-ish or adjacent areas in TN, KY, AR and maybe GA, and make one distinct change: put a large sign on it that says “CAMERA ONLY CAPTURES FOOTAGE OF SPEEDERS”
I’d guess it’s less than a week before somebody figures out driving slow also helps with aim. Would be an interesting study I think. Heck, I’d put one in my garage as a souvenir / warning about reality.
It's basically just this. The authorities have an incentive to make speed limits lower since it gives them more speeding ticket revenue, and the insurance companies go along with it since they can charge you higher premiums if speeding is on your driving record.