What stopped them is that the entire rational for Zillow's approach is that human appraisal isn't needed. An algorithm, they think, should be able to do a good

What stopped them is that the entire rational for Zillow's approach is that human appraisal isn't needed. An algorithm, they think, should be able to do a good enough job. Any individual person who, when presented with this scenario, thought they should have brought in a human to look at the house does has been selected out of working for Zillow.