I'm a Parks Superintendent for a city of 200,000, and have been a runner for 40 years. There's a number of reasons why public drinking fountains are becoming less prevalent.
1. Vandalism. It's really depressing to those of us in the business, but the lack of respect for public parks in the U.S. is appalling. Today I stopped by one of our drinking fountains on my 14 mile run to find all the drain holes plugged with bark mulch. But at least they didn't plug the spout so it still worked. Many get filled with sand, rocks and other debris. Other times, they break the handles.
2. Fountains are expensive. A typical high/low dual bowl fountain costs upwards of $5000. Nothing in the park business is cheap. They also have to meet stringent ADA rules for height, access and button pressure.
3. Water quality rules also come into play. Water for fountains has to come from a domestic line, separate from irrigation, with its own backflow device. Many old fountains were connected to irrigation lines when the water source was treated domestic water. Can't do that any more.
4. Fountains also have to drain to a sanitary sewer or other drainage system. In some areas, you can't just drain them to the nearby creek or planter bed anymore.
5. Yes, they are a bitch to maintain. Cleaning sand traps and filters, fixing valves, replacing backflows that get stolen for salvage, all are reasons why they're going away. Many parks agencies lost half their staff in the recession so they prioritize what gets fixed.
6. And finally, as mentioned, people now carry bottles everywhere. So now the trend is to do away with the standard fountain and install jug fillers instead.