You and I may be happy with this. But a lot of people will not. People need a sense of purpose; a desire to be needed; to be valuable. Some may find value in free time to pursue artistic endeavors; many will not.
I think you are seeing this backwards. From birth to probably a little bit after college, the majority of people are perfectly happy to amuse themselves with "hobbies", regardless of the wealth generation (or lack thereof) of those hobbies. And yeah, a hobby could be productive, but it doesn't need to be.
Only after working 9-5 for a few years (and likely becoming more and more responsible for themselves), do people start to forget how to naturally find curiosity or amusement in the moment. I know many adults that literally can't sit still for a 2 hour movie, they have to get up and fix something, or clean something. But those adults didn't used to be like that, they used to be able to immerse themselves in something creative or otherwise pleasurable for hours at a time.
So a universal income would allow many people to (likely gradually) return to that mindset they had when they were younger. Letting their mind go where it wants to, instead of having a constant stressful feeling that they need to "get something done".