It only 3d prints the walls, which are far less than 95% of the house. The walls are concrete, which cannot be smoothed or nailed into or have cabinets hung on without significant human labor. Cracking and weather sealing is a big problem. It's not even cheaper.
The big examples that people have done are frequently not even real (prefabricated elsewhere or touched up by hand), and never include a 3d-printed 2nd floor, because that's not possible to do.
Or perhaps just the term is misapplied. I saw a really cool video about... basically robot concrete pouring & shaping... built 95%+ of the house in an automated way (once a human drove the truck there).
Maybe not economically reasonable where you live or whatever, but I see nothing fundamentally wrong with the approach.