Pools are expensive to build and they almost always need chemicals and filters to be safe to swim in making them expensive to run. Where there are natural lakes/streams/ponds they are typically safe to swim in and much cheaper.

Which is to say anywhere pools are the primary place people swim, they will be few, small, and generally overcrowded (and also expensive). If you live where there are natural places to swim you will generally find it better, but many places don't give you those options.