Naive follow-up question: why does such a person need to live in the bay area? If you're living off disability, why would you try to do it in the most expensive place in the country? Is community that important?
I realize this line of inquiry sounds callous ("why can't they just save some money?"), but I genuinely don't follow why somebody with a regular income who's not tied to the bay area by a) drug addiction, or b) a job would put up with homelessness to stay there.
I find this confusing because you seem to imply that having an income makes you ineligible for social security retirement benefits. But as long as you are 65, you're eligible without income caps. There's no requirement that you're not working.
Social security disability checks do require that you're not working. Is that what you're talking about?