The point isn't to offer people enough to survive so they can withdraw from the workforce, VLM. The point is to provide a subsidy to income - which I hope is means tested - that covers essential cost-of-living expenses. Primarily, that which an economist would define as a need over a want. Now, to "so what if they do?" If the safety net is replaced by UBI - which is broadly the intent - people who are vulnerable and reliant upon UBI have no viable way of accessing essential services like health care because they've not rationally treated the funds. Homo Economicus is not a real creature. So, the most vulnerable not only remain vulnerable but arguably worse off than before because they're in trouble and free-falling due to the absence of a viable safety net.