Framing lumber’s are much easier to work with, readily available and for the most part still the most inexpensive way to build. While metal framing materials can and usually are less expensive than traditional wood framing materials, Metal framing ends up costing more. For example; standard sheathed Romex wiring can be used in traditional wood framed structures ( with the exception of multi dwelling, multi stories, and varying city building codes ) while metal constructed structures require mc ran electrical. Places like Mexico and several other countries rely mostly if not completely on concrete materials for constructing dwellings!
If you do an Internet search of different building construction methods you’d be surprised how some companies are doing it. From plastic molds, concrete walls to pre fabbed houses!! Hope this makes some sense!