It's less 'should' than that UBI enables the possibility of reversal of the long term rural -> urban migration trend, since this trend is driven by job seekers. I don't think it will occur (the lower your income, the more you rely on geographically-based support networks) but if it doesn't, then UBI increases will be largely captured by rentiers. If it does, then urban rentiers will have to compete with non-urban rentiers, and UBI will have a chance to have the economic effect intended by proponents.