Someone might (quite reasonably) become fed up with work; that is a reasonable presumption.
Where I think you're making an unreasonable presumption is in that fed-up person throwing the working towel in altogether, and sofa-polishing for the rest of their days.
I contend that, with the security of a UBI, most will (upon becoming fed up with bus driving, as an example), move into parks maintenance, or mentoring disadvantaged kids, or social care...................
It could add up to a more flexible, responsive, and nimble workforce, better able to meet the demands of the economy at that particular time.
To the benefit of us all.