And now you do the same with pumping water back and forth... I get it that trains are handy when you have plenty of space and lack water, but many, many places around the globe lack the space for the hughe amounts of train tracks running up a 1000 meter high hill.

In addition, take into account the enormous amount of moving parts. Maintenance everywhere! Compare the tracks with carts to a large pump/generator and pipelines with water I guess the latter is much simpler to maintain and better looking to the eye. While train tracks should be kept clear of people you could easily see people using the lakes up & down the mountain for recreation.