Pumped storage seems to fit the need pretty well, in that it’s trivially easy to build and there are hundreds of thousands of potential sites in the US alone.
Yeah, but plenty of people don't live in the US and their geography is much less suitable for pumped storage than the American (or Norwegian) one.
For example, Finland is very flat, so are the Baltic states and most of Poland. So is Bangladesh, which has three times as many people as all the above together, and a nascent industry that needs energy.
In Czechia, we have rolling hills that are suitable for some pumped storage, but we built up almost all the good locations. In one case, an entire top of a mountain was cut off in order to make a reservoir:
https://cs.wikipedia.org/wiki/Dlouh%C3%A9_str%C3%A1n%C4%9B_(...
There was an interesting proposal for a massive pumped storage Strathdearn[0]
It has the capacity of about 6800 gigwatt hours (283 gigawatt days) which is about 1000 times the existing scottish current pumped storage in Cruachen.
The article claims to cover the existing daily power requirements of UK and be able to export to europe.
I am not a civil engineer or geologist so it might be too big, not practical and too expensive. lots of smaller schemes might be better, but an interesting read
[0] https://scottishscientist.wordpress.com/2015/04/15/worlds-bi...