How is a thing which half the population doesn't have the disposable income to participate in "effective" in addressing income inequality?

The survey is classic selection bias.

Anyhow, it does not distinguish between "has no discretionary income" from "spent every dime they have". The latter is a common problem even among higher income folks.

People seem to be able to find the funds to buy iphones/booze/drugs/airjordans even down to the lowest levels.