I think the reason is, pumped hydro competes with fossil fuels as a storage mechanism, and it's very hard to compete with fossil fuels as a storage mechanism on economic terms. In terms of clean tech, it's probably still the best in pure economics, but batteries are currently getting more attention because Tesla found that by bundling its batteries with wheels and motors it can sell them as luxury goods. That circumvented the need to store energy cheaper than fossil fuels, but it's obviously hard to do anything similar with pumped hydro storage.