Notably, the report was published in 2015.

As you said, the story is complicated. Even in 2015, a decade ago:

> There is one other stark difference: only upper-income families realized notable gains in wealth from 1983 to 2013.

During the period of analysis then, either consumption among the lower two tiers eliminated their available savings ability, or the real purchasing power over this period declined, leading to the same effect.