[Closed] Traffic Cameras - why not?

There might be a simple answer to this, but its something I'm struggling with. As has been mentioned recently on threads-a-plenty, as commuting cyclists we see many drivers on their phones and / or driving terribly (some cyclists are also idiots, I know). It is a guaranteed thing that I'll see *something* naughty on every commute journey I make. A lot of this could be caught by camera, especially the speeding but also phone use.

Which puts my mind back quite a few years to when speed cameras were commonly installed on roadsides and swiftly a) caught loads of people, b) brought in the money, c) (I think) got slammed and largely removed because of b. Why was this? I only have Mail headlines ringing through my mind about police forces raking in the cash and boo-hoo it wasn't fair because the poor speeding drivers didn't know the cameras were there. Is that right?

So it strikes me, still, that cameras are the way forward. Police forces are strapped for cash so don't have the manpower to be out enforcing this. Is it really some pathetic excuse about cameras being unfair that stops them being installed? Even if any funds raised above and beyond the costs to install, maintain and administer them are put to good causes (like road awareness / sustainable transport charities)...? Why is not this simple?