Why waste energy on a system that's designed to grow increasingly inefficient over time (Crypto PoW mining), when you could simply store the energy or use it on something that is helpful to the local community, as in food or manufacturing?
Because the whole premise is that you don't really have a way to store or use that energy in other ways. Then converting it into cryptomoney makes sense- then you can use that crypto to buy things which are helpful to the local community- even things that are produced on the other side of the world, where your energy could never reach.
An interesting thought is that of using that crypto exclusively to buy energy when the prices are non-negative. But I'm not sure that makes sense from an economic point of view, it's a snake biting its tail.
Depends of your investment. You could always deploy on those sites old miners where the ROI is already paid off - so it's always better than them being thrown away.
You can move miners easily between inefficent sources of energy. Water, dams, etc... not that much. Using current battery technology would be too nefast for the environment.
