Also, getting rid of gigantic perverse incentives induced by welfare thresholds helps people find their way back into the working world. UBI isn't about making poverty more desirable, it's about making poverty less sticky.
The difference is the same as having $0 and having $20,000 in monopoly dollars.
The number printed on the notes is irrelevant, the only thing that matters is what you can get with them, and if an apple costs 20,000 monetary units because there is so much money in the system (as it does in many countries) then everything else readjusts to match those levels.
But there’s a pretty big objective difference between the poorest person having $0 and the poorest person having, say, $20,000 a year.