In terms of city government unionized labor salaries and equipment cost, or hiring a contractor cost, it can be VERY expensive per meter to dig up an existing concrete sidewalk/curb and road to run code compliant AC electrical to a parking meter. Or something like a bus stop arrival time sign. Looking at $20,000 per unit in some cases, or more. And then there's the question of where do you get the AC power from in a built up downtown type area, you can't just tap into the nearest building, it usually involves dealing with the electrical grid for the streetlight system which was not designed to support thousands of small accessory loads hanging off it.