Gary Burtless writes:
Instead of subsidizing low-wage employers, most [government] assistance programs reduce the availability of low-skill adults who are willing to work for low pay and lousy benefits. By shrinking the pool of workers willing to take the worst jobs, the programs tend to push up rather than push down wages at the bottom of the pay scale. Low-wage employers do not receive an indirect subsidy from the programs. Many must pay somewhat higher wages or recruit more intensively to fill their job vacancies.
There is much more at the link, including a considerations of programs which are an exception to this generalization, such as EITC.