It assumes that individual income is the overwhelming determinant of quality of life. This is not a material concept. Ensuring a decent standard of living is one way to help achieve it, but it's not the only way, and not necessarily sufficient. Politically, of course, low-income workers are a much more appealing constituency than welfare recipients. Workers' compensation goes to workers.
Unemployment compensation is conditioned on prior participation in the labor force.
The earned income tax credit, which has ballooned into a large new entitlement, is by definition available only to earners. Food stamps have an independent farm-state constituency. They've probably never been as unpopular as AFDC, but neither have they ever been as widely accepted and unstigmatized as Social Security pensions. Given the booming economy, it's been relatively easy for governors to push would-be aid recipients into the labor market and take credit for the resulting caseload decline. But policymakers will eventually face some harder choices.