It is simple: speeding tickets are a revenue stream.
EDIT: as a thought experiment, imagine that we went full cyberpunk hell-future and they started letting private equity companies put up cameras anywhere some MBA thought their cut of the ticket revenue would pay for the camera. How many speeding/stop sign/red light tickets do you think the average driver would get on their way to work? Now ask how different that is from the average driver's experience almost anywhere.
This translates to: we don't care you're not going to drive here again, or that you didn't notice the sign. We don't even care if you slow down or not.
Not being sour here. I got caught at a well signed area in my local neighbourhood area - now I'm driving there slower.