Nature is a harsh mistress and we've abstracted a lot, but not all, of that away.
And of the ones who wouldn't, what would their reasons be? For some, I can imagine a great taste for art and travel and appreciation, which isn't "productive" per se, but is self-motivational. For others, perhaps trauma of various kinds makes the prospect of producing anything and subjecting it to scrutiny overwhelming.
I'm sure there are some people who truly are just plain lazy, but I think if people truly don't want to do anything, there's usually a reason, and if that reason were overcome, most people, just because they're humans, would want to do something.
I have to disagree about hobbies, though. I think a lot of people intentionally choose not to monetize their hobbies, lest the pressure of making money infect the joy of the hobby itself.
Not everything is about abstrac economic value. Humans have other needs which need to be met, like social interaction and leisure.
Now maybe that price is indeed worth it, but I think that's a decision that should be left up to each individual, not imposed at the societal level via UBI or something similar. If any particular person decides it's worth taking the economic hit in order to work less, or on something that's less economically valuable, that's completely up to them.
I really wonder too. I like UBI for example for this reason. I'd think addictions would wreak havoc among these people too though, because addictive things wait around every corner of society, promising to make the bad feelings go away. Nevertheless I think it would be a worthy effort to have a system that doesn't let people stoop down below a specific level.
It helps that I'm paid for work that I'd otherwise been doing, but I have a decent history of working less great jobs because I find the prospect of overcoming challenges, that I'd not put upon myself, satisfying.
I'm almost 50, and have been working full-time since I was 17. Yes, full-time, even during my five years as an undergraduate. Even when I hated the work itself, I have always made the best of it. I worked in over 30 restaurants around the US for about 10 years, and had a great time of it, even though the work was horrible, grueling, and often with people I could not stand.
Now I work in software development, and love my job. It's stressful as heck, often frustrating, but rewarding in many ways.
Check out Karma Yoga - it's close to how I've always felt about work. Incidentally, I have no personal connection to Hinduism:
Don't think it's a capitalist thing.