Accident figures peak.
Council installs "safety" camera and lowers speed limit.
Next year figures revert to mean. Council: "Aha! The lower limit and camera has cut accidents, we'll make it permanent".
Net result: speed camera in middle of nowhere, on a dual carriageway, in isolated section of 40mph limit. Often on a bend.
Goodbye 85th percentile rule in yet another spot. I can see why that's unpopular. Yet the spots that really should have cameras near schools, or in other spots around town, generally don't.
In many places (including Ireland, where I live) the same roads where people drive are where you walk your dog or ride a bike - with no footpath. The 85th percentile guideline doesn't help them.
Remember that roads were for walking (by humans, horses, etc) and drivers turned up and stole them.
On dual carriageways, which is about the only location I ever feel annoyed by speed cameras, it's a fairly reasonable basis for setting limits. That's the situation you find reductions of limit, with associated speed camera, that are simply unexplainable from road conditions, and lack of sources of danger, risks such as built up areas etc.
https://www.google.com/maps/@52.65301,-2.0079976,12.25z
That's the M6 toll, a road the folks who control such things would like you to pay them money to drive on. Note that it runs beside the perfectly straight 4 lane A5, which predated it, and, simultaneous to the toll road opening had its speed limit reduced to like 30 miles an hour and speed cameras installed every 200 yards along the entire length.
Hard to imagine the whole thing became that much of an accident hot spot right at that moment.
They're still very unpopular.