I feel like your underlying assumption is that "if UBI leads people to leave their jobs, UBI has obviously failed", whereas it's literally the very goal of UBI to reduce (or even eliminate, in the case of "full" basic income) the need to hold a job just to have enough income to merely survive. You can argue that's a bad goal if you want, but expecting everyone to continue working despite receiving free money is kind of missing the entire point of handing out that money.
Btw, just because people act a certain way in a short period of time (especially during a time that was so out of the ordinary) that doesn't mean they'd act the same way for ~half a century. Sure some fraction of them might, but lots of people would get bored and try new things. Having nothing to do for months or even a year or two can be fun and exciting for some, but that doesn't mean they'd love the idea of having nothing to do for the rest of their lives. People get bored, people want luxury, people want variety, people want fulfilment, people have kids to raise, etc.