One’s career is rarely a vocation.
It is not the norm for workers to be filled with purpose by their job; it’s the exception, and one accessible only to those lucky enough to have a lot of freedom to choose positions.
People who have a sense of purpose will work toward it for free, if it doesn’t interfere with their ability to live comfortably (and sometimes even if it does). This is, after all, what hobbies are: situations where someone spends money in order to do work that nobody is willing to pay them for, simply because they enjoy working.
The typical worker is performing tasks they despise in order to earn barely enough money to eat. To free them from that toil without taking food out of their mouths is a mercy; it gives them the opportunity to persue a purposeful life.
Right now, all economic and social incentives are focused on automating the position and simultaneously removing the income, replacing it with nothing. This is cruelty: we’ve taken a person who could already barely survive, and while we’ve removed their ability to survive slightly better by performing a task that makes them miserable, we’ve simultaneously stuck them in a situation where, in order to maintain their ability to eat at all, they must show proof of looking for work while avoiding actually finding any; after all, getting back a job equivalent to the one we automated away means having no income between the benefit cutoff and the first paycheck, and since they were prevented from accruing savings, it means weeks of not eating. UBI targets the welfare trap and eliminates it, making changing jobs less risky for everyone.