Open Question: What does this economic chart show and what, in your opinion, is the likely explanation for it?
I think the reasons for the divergence of productivity and income can be summarized as globalization, modern technology, inequality, decreasing bargaining power of workers, and economic policies. This divergence is likely to continue till workers will be considered redundant and unemployable who should be fed through UBI in order to prevent social upheaval for smooth transition towards technological singularity.
I guess those humans who will receive UBI will be the last humans.
@Carbondate - How much of this do you 'blame' on tax policy?
Technological advances have led to increased productivity, but not increased opportunity. Our nation's political and business leaders have failed to plan for the changes that enhanced technology would present. Ideally, there should be new jobs opening to support this new technology, but there hasn't been.