Basically it comes down to the cost of being wrong. If you decide that someone is dead and stop sending checks, you might learn otherwise when their congression

Basically it comes down to the cost of being wrong. If you decide that someone is dead and stop sending checks, you might learn otherwise when their congressional representatives or reporters start asking why you failed to perform your legally-mandated duties at great cost to the retiree. Mailing a check is a lot cheaper than getting in the hot seat because you cut off some disabled veteran’s rent. Older people often have disabilities or care situations which make contact less reliable, they’re more likely to use cash or have relatives do their shopping, etc. so you’re left with relatively slow or expensive options like paying people to visit in person (which has all kinds of problems around privacy and access - Social Security has a legal obligation to serve someone who lives abroad, on a reservation without paved roads, etc.) and any other kind of verification system won’t help with fraud since people collecting their dead relative’s check can also fill out a form or answer a phone call fraudulently.