Mostly inertia. The 14-gauge Romex in your walls is big enough for DC LED lighting as long as your lights are on separate circuits from your wall outlets and th

Mostly inertia. The 14-gauge Romex in your walls is big enough for DC LED lighting as long as your lights are on separate circuits from your wall outlets and the voltage is around 24VDC or more. And we need lighting power supplies that can change 24VDC to constant current, but those are simpler than the 120VAC-to-constant current supplies in light bulbs now. For power outlets you probably need at least 12 gauge wire and 48VDC. And we need a new standard DC smart outlet that can negotiate with the load and locally buck the voltage down to whatever the load needs. All this is easier with new construction than with retrofitting of course. Then it's a chicken/egg problem: We need lights and appliances built for this infrastructure but we need the infrastructure before anybody will build devices for it. The solution is to build bridge devices that can replace wall warts that negotiate with smart outlets. Lights are trickier: Someone's going to have to build "raw" LED "bulbs" that assume the power supply will be added elsewhere. I've already started retrofitting my table lamps but the rest will be harder.