Because the purpose of police cars and and speed cameras, is ostensibly to make you slow down to the speed limit. Marking these on your map, makes you slow down.
This probably varies country by country, depending on whether it's a money-making exercise (where the police try to hide) or safety (where cameras are painted bright yellow and the police are clearly visible)
...this also varies by country: in some countries, the speed limit itself, not the camera, is there for your safety - I mean, how many cameras should they install?! In others, they exaggerate the speed limit, e.g. 50 km/h on a straight road outside of built-up areas, hoping that drivers will at least slow down to 80 km/h (looking at you, Italy!).
I guess the future of speed traps is "section control", e.g. install cameras at beginning and end of a speed-restricted stretch, and if the time you needed is significantly below the expected one with legal speed, you get a ticket.
> I guess the future of speed traps is "section control", e.g. install cameras at beginning and end of a speed-restricted stretch, and if the time you needed is significantly below the expected one with legal speed, you get a ticket.
This has been common in Western Europe for decades now.
Anywhere with electronic tolls already has this. It would be trivial for politicians to hit everyone with a speeding ticket on a tolled highway if average speed between two tolls is more than legal limit.
This probably varies country by country, depending on whether it's a money-making exercise (where the police try to hide) or safety (where cameras are painted bright yellow and the police are clearly visible)