because there's no single DC voltage that all devices use, so you'd end up with homes wired with 48VDC and many power brick/wall-wart dc-dc converters to obtain 24VDC, 19VDC, 17.5VDC, 12VDC, 5VDC, etc.

and the cable gauge would need to be incredibly thick to avoid significant losses, DC does not go very far distances well at all. Be ready to pay for #2 gauge copper in your walls instead of 14ga.