This confused me as well. In the article, there's the criticism that by not being allowed to charge for electricity what it cost to generate, producers have fallen behind on maintenance of their plants. But I don't see how that follows from deregulation. When I think deregulation, I think something more akin to, "Alright boys, you're on your own. Ya'll will live and die by your ability to profitably generate the power people need and want, and deliver it how they need and want. Don't get lazy now, or some whippersnapper will buy your infrastructure for pennies on the dollar after they bankrupt you because all your customers went for their better customer service."
Not being allowed to charge actual cost of production strikes me as something that would come of price controls, which are a kind of regulation, not deregulation.