The generation capacity will idle otherwise. It's probably better to sell the electricity for cheap than let the capacity idle to the point where it rusts and becomes useless.
Oh, it won't idle, no worries. They're running as hard as they can. We use the 'leccy to produce the world's cleanest aluminium, nickel, silicon etc. These industries are what drove construction of the hydroelectric plants in the first place.
People are talking maybe we'll build the next gigafactory for batteries here. There is no shortage of electrochemical industries hungry for that power, and that green image.
