Most of the things that are productive for society require study and practice of skills that aren't particularly interesting to the vast majority of people.
>Sure, these things aren't economically productive
The vast majority of things that are productive for society are economically productive. That's why people pay for things.
We don't need UBI to go toward funding artists and musicians. That's a waste of resources. Particularly considering that far too many people are likely to choose the easy way out, pursuing "what they love", i.e. soft skills like art and music. You also drastically underestimate the number people who are perfectly content with doing drugs and watching TV/playing video games all day.
Unfortunately while resources are scarce, human nature is such that people require incentives to do the things that need to be done.