You gotta remember here, Nall's in his human form - which is probably only slightly stronger, physically speaking, than stock human. And the mysterious package is an iron-bound chest full of hot coals and a dragon egg, unless I miss my guess, so you can figure it's got some weight to it in addition to being rather difficult to handle. Would -you- wanna haul that up infinity-plus-one stairs?

Besides, he'd have to destroy the house to rewire it, and they -just- got the wallpaper right...