There's plenty of alternative house designs (especially for tiny houses but also full size) that could be far cheaper than 3D printing, and are often made from recycled materials, such as container homes. There are outdated regulations that protect the housebuilding industry, or laws that literally ban certain types of structures. There's also the issue of current homebuilders just not knowing how or not wanting to put up designs they are unfamiliar with. This problem was known way back with the Buckminster Fuller Dymaxion House.