But, of course, when demand goes up, prices go up for everyone; more demand isn't going to lead to the creation of more natural resources, so the benefits of cheap hydro are limited, and usage of them is a zero-sum game. Power companies have no incentives to discourage crypto miners, because obviously increased demand leads to more profits for them, while meanwhile the externalized costs are being paid largely by households and small local businesses.
You could make miners pay more for electricity, but unless you charge them so much that it's no longer profitable and they go away, they're still going to be using that electricity, to the detriment of everyone else in the area. Better to just ban them entirely, IMO, but it's pretty hard for politicians to just unilaterally kill off entire businesses, even bad ones like these.