WASHINGTON – In the aftermath of storms that knocked out power to millions in the Midwest and Mid-Atlantic, sweltering residents and elected officials are demanding to know why it’s taking so long to restring power lines and why they’re not more resilient in the first place.

The answer, it turns out, is complicated: Above-ground lines are vulnerable to lashing winds and falling trees, but relocating them underground incurs huge costs – as much as $15 million per mile of buried line – and that gets passed onto consumers.

With memories of other extended outages fresh in the minds of many of the 1.26 million customers who still lack electricity, some question whether the delivery of power is more precarious than it used to be. The storms that began Friday have been responsible for the deaths of 24 people in seven states and the District of Columbia, including a utility contractor who fell to his death Monday in Garrett County, Md., while removing limbs from a storm-damaged tree.