Although not mainstream, I think you'd be surprised as to how much construction today uses SIPs (structural insulated panels.) Made in the factory and delivered on the back of a truck. Usually higher-end property, but certainly becoming more popular with volume builders (economies of scale.)
For really high spec, think of Huf Houses in Germany. For lower-end stuff, the savings would be considerable. Traditional building sites can be among the most inefficient "factories" imaginable - all "wet" trades, and having to handle mountains of heavy masonry. Plus the interminable delays ........ not to mention our weather.
We do still go all misty-eyed over cob and thatch, especially down here in Devon. I still enjoy working on it, but it belongs in the past ........ along with concrete blocks ;o)
It'll all come around in time, Hammers. It just takes a long time in this country. As with everything, it'll be cost-led... so, inevitable.