I agree with you. People need purpose. Ever owned a Border Collie and spent a couple days without giving it something to do? It's bad for the dog and dangerous to your home.
So yeah, even if no one ever really enjoying being a gas station attendant, getting up and going to a job to earn money and pay rent gives people a sense of purpose. And UBI definitely risks robbing people of that purpose. The alternatives to UBI soon though might be creating fake jobs or letting people starve.
What's unfathomable to me is that so many people seem to believe that a sense of purpose can only be derived from need.
Humans aren't like that. They don't deprive themselves of activity like a bored dog unless you (who?) give them a job. If you give people their time back, they will fill it out with whatever they actually want to do, and that's freedom.
Conversely, the erosion of free time over the past generation has arguably also eroded the social structures that keep people healthy.