Simply that mining has become so competitive, miners cannot afford to consume the same electricity as you and me. To survive, they must contract for wasted, stranded or off-peak sources of electrical power. Isolated dams, solar and wind arrays, methane gas at well heads, excess nuclear, off peak vrid power, etc. This means that market forces naturally channel miners to use up only the electricity that no one else can use. Those that attempt to compete with your clothes dryer go bankrupt quickly.