I've noticed the same thing. I've been riding in the same area here for almost 30 years and the number of water fountains has gone down. We have large parks with playgrounds and ball fields with no drinking water available, and I've been known to stop in the public bathrooms at these parks to fill up my water bottles in the sinks. Gotta do what you gotta do.
Why? My guess is that they're too expensive to install and maintain.