You know what else they could do? Store it... in batteries... which are reliable for long term storage... and aren't nearly as volatile... and use it on stuff that generates more value per watt consumed...
For example, batteries can be used to power homes and businesses, which can help to reduce reliance on fossil fuels and improve air quality e.g. improving quality of life which generates a shit load of value. Batteries can also be used to provide backup power in case of a blackout, which can be essential for critical infrastructure such as hospitals and data centers. I just don't see how most crypto currency can compete in this space... maybe something highly power efficient? But even then the value is extremely volatile.