To run these otherwise hibernating electricity factories the utilities need to make sure there is enough fuel sitting around ready to combust, to turn turbines that turn crankshafts that spin inside electromagnets that pulse vast quantities of electricity out into systems built to move less of it. They need enough trained staff on call and ready to go to fire it up and keep it running, and they need to ensure that it is in good working order despite sitting idle most of the time. This is massively expensive for them, and it is a simple and constant drain on their bottom line.
