To understand rising inequality, consider two janitors

This article does a good job of answering one of the questions of "Where is this inequality coming from?"

The short version is that even though a janitor makes a comparable amount in take home pay today as they did 35 years ago, structurally today a company hires their janitors through a service, not directly. And as such the people doing the work don't get the other benefits that full time staff of the company hiring the service do.

As a result, improvements in working conditions that were won by Unions in the 60's and 70's have been completely erased for those people who can be employed indirectly.

It is a part of the problem I hadn't considered and it raises a lot of questions.