I have lived in places where the speed limit is very obviously around 10 mph too low for the road's engineering and surrounding environment, consistently. Consequently, there is truly no one during busy times doing the speed limit.

This gives police the ability to pull over anyone, at their discretion, with direct legal cause (not even the "immune from consequences in practice" kind). Even driving the speed limit creates a hazard and merits intervention according to the law.

The place I'm describing was very racist, driving while black was absolutely unofficially illegal, and this lets cops pick and choose in all the worst ways.

Be deeply suspicious of any law that is routinely broken by everyone for years with no change - it is to allow arbitrary, bigoted enforcement.