Second, automation. Robots have been enormously successful at removing labor from assembly lines. They are good at repetitive, manual tasks. So a GM plant that used to employ 75,000 workers with middle class wages, now employs 7,500 at lower wages. The robots that displaced the labor don't buy things at Walmart or pay taxes.
I was surprised to see so many people in the film I know or know of. @afisher 's previous business partner had some really cogent explanation of the rise of income inequality:
He said automation is replacing labor with capital so the people with the capital get richer and labor gets poorer. It leads to this graph, which shows the rise of the rich and decline of the poor. Guess which color is which...
Here's the thing: robots displace labor, but AI displaces white collar jobs. It's another form of automation, for a different class of workers.