Pumped hydro is great but unrealistic in many countries. You need hills or mountains with space for new lakes. All obvious places already have them, for the others the ecological impact often is quite significant.
The country point is interesting, so the market is countries lacking topography suited to hydro plants? How big is that market really?
And considering that pumped hydro is currently the only viable grid scale energy storage mechanism (inb4 but li-on), those countries currently either 1) share a grid with neighboring countries that do have pumped hydro, or 2) forego energy storage altogether and use peaker plants like everyone else. If you do 1 you better trust your neighbors to never go to war with you, otherwise you better have 2.
So the market is: countries lacking topography suited to hydro plants, who currently share energy storage with neighbors who they don't trust, and who for some reason aren't just building peaker plants (which are essentially just normal fossil fuel power plants) and are holding out for a non-extant technology to be developed.
I'm not much of a capitalist myself, but even I can tell that that's a bad investment.
Hydro plants are built reversible whenever possible. The ones that aren't ("run of river") are that way because it was impractical to impound storage.
If a hydro site is convertible to reversible, chances are it’s been already. Most sites are not really suitable because regular hydro plants don’t need a lower reservoir or water source and so can be built in locations which don’t have one.
Meanwhile pumped hydro can be built in locations where normal hydro makes no sense because there is no natural downflow or upper reservoir e.g. Taum Sauk.
> All obvious places already have them
That is, we’re already practically at max capacity for hydro.
https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...