An unfortunate extension of this is that sometimes, a speed limit will be set very low for no apparent reason, and
almost everyone will exceed it significantly if it's not visibly being enforced. This puts a driver who wants to be both safe and legal in a no-win situation.
Personally, I liked the idea put forward by one of the UK driver advocacy groups a long time ago. Speed enforcement measures should prioritise places with a dangerous hazard, and there should be prominent warning signs on approach in a standard format that show (a) the speed camera sign, (b) the current speed limit and (c) the nature of the hazard, so drivers understand why the limit is there and enforcement is visible and clearly justified.
Somehow, I suspect that if drivers had more trust that speed limits were being set appropriately and expected that they would actually be enforced where they most matter, they would become largely self-policing anyway. Then the actual road police could spend more time dealing with other problems like using a phone behind the wheel or drinking and driving, which are potentially more dangerous than most speeding but much more difficult to enforce without human intervention.