I’m not sure the situation in Sweden, but usually the easily developed hydro sites have already been built, and any remaining sites will be quite expensive compared to power generated. Additionally, climate change can threaten the reliability of hydro as snowmelt and precipitation become more unpredictable. Also, they generally have a fairly large negative environmental impact aside from climate change.
I’m sure there are some projects that will pencil out but probably not enough to decarbonize the whole energy grid.