Considering the enormity of households in America, and in the general population, paying rental stipends to the landlord. If a general relief law paying a guaranteed income were in effect now, the entirety of it naturally is vacuumed into the landlords' pockets?
The history of capitalism is littered with reform efforts inherently partial, incomplete, and dependent on other aspects of capitalism in ways that make them ineffective if not counterproductive. This is because the reforms are usually produced if and when pressure from capitalism's dysfunction forces "something to be done." Reforms are what capitalists always prefer to any questioning, let alone change, of the system itself. Your email raises an important question about how capitalists and others might respond to initiation of a UBI. Your question is right, but only one of thousands of responses that could serve to nullify or even reverse the results of a UBI law etc.