The unsubstantiated claim is "writing must be financially incentivized". That's not my claim to substantiate.

If you think that claim is somehow self-evident, it may be worth considering your biases.

That's pretty clear. I start from "work should be financially incentivized" as evidenced by, well, the world around us. Then you argue that writing is very special (maybe a form of art, and many artists are hobbyists). To which I reply that while writing could be considered a form of art, the kind of books I read (and sometimes write) require hundreds of hours of work (that could be very satisfying, for sure). The enormous time investment means that you either get money for it in some way or you don't do as much of it as you'd want to, because you need to get a paying job to survive.

> you need to get a paying job to survive

Exactly. The idea that people who have an ardent need for financial support to survive would choose an activity that is statistically unlikely to provide sufficient financial remuneration seems odd, don't you think?

The separation here is nothing to do with "art". It's to do with a person's ability to choose an occupation based on desire/interest or pure financial need. Writing is in the former category not because it's "art", but simply because one needs to be comfortable to have the luxury of taking such risk.

To put it another way: people choose the vocation of writing despite financial motivation to pursue alternative more lucrative undertakings.