Land is more or less worth the same whether it has a used house on it or if you build a new house on it. The trouble remains that the high cost of new construction anchors the cost of used houses.
Construction costs should really have been driven down by the march of technology, but that really hadn't been the case. It's mostly stagnant IIRC. But construction costs doesn't really explain the housing crisis well.
The majority of the cost of a home in places with shortages is the land, not the home.