But perhaps that's exactly where we need investment - to figure out a way to apply automation to adobe type building?
Unfortunately this isn't the kind of thing the market is good at sorting out, but there could well be some breakthrough tech that makes adobe building cheap. We just don't look for it.
There have been attempts over the centuries. Rammed earth walls attempt to do away with the "dealing with lots of relative small pieces" problem (adobe bricks). But they require form building, which adds a significant labor component that isn't there for the "lots of small pieces" approach.
Unfortunately this isn't the kind of thing the market is good at sorting out, but there could well be some breakthrough tech that makes adobe building cheap. We just don't look for it.