It works very well, not disputing that.
But, like geothermal power generation (which is also very good), it’s extremely dependent on location. Most populated areas don’t have the altitude differential (steep hills) and/or water supply to implement pumped hydro storage.
Where it can be used, it should be (and largely is - fossil fuel generation does better with some storage as well, since demand is not consistent), but it’s hardly something that can be deployed alongside solar and wind generators everywhere.