Replacing ungrounded wiring is quite labor-intensive. It can also be the most expensive thing to replace in your home, because as the wiring must be upgraded to the current codes that older homes typically didn’t follow, as well as being completely replaced.
Additionally, great care must be made to fish wires up and down finished walls to refeed wires. In several cases, holes may have to be cut in the finished wall in order to get wires to where they need to go.