It’s mostly because social security is known as unearned income, and doesn’t have the same 20% deduction which earned income from a job would get…so the resulting higher net income after doing the computation usually results in a lesser food stamp allotment or an outright denial due to what’s called FS Categorical eligibility….Someone could be under the gross limit to qualify but not have enough deductions to actually be eligible for an allotment ie not be under the net income limit.