At some point, it becomes a business for every dev.
Since I read your original statement as a general observation more than specifically pertaining to this game and answered in this vein: it certainly does not for every dev. The vast majority of devs don't even make $100 per month. That can only be a hobby with some nice trickle of money, but not a business.
It's a lot of work. And devs that can't make their games a business, sooner than later abandone them. That's why there are so many abandoned games here.
While that certainly is an aspect, I would guess there are other points which are more important for the number of abandoned games. My personal guess is "people who completely underestimated the scope of a multi-year project, and possibly overestimated their own abilities when setting the scope of their game." Got no data to back that up though.
And, after all... 'brainchild'? This game? I don't think the dev considers his 'brainchild' all the filling material in this game, all the dull conversations at breakfast or while watching television, all the childish and silly situations, or the vanilla sex scenes. Let's face it: at least half of this game could have been written by an AI, just with a few tweaks here and there from a writer. Probably way more.
First again: I wasn't talking about this game specifically but games in general. Second: we will have to agree to disagree on the merits of those small discussions, I think many of them add flavor and life to the world. Even the ones where you have three options which change nothing but two lines of dialogue.
But more importantly: yes, many people are proud of their work, even if better works are easily available. It is their song, even if only five friends will ever listen to it, their painting, even if any schoolchild can paint at that level if only it takes the time, or here: their game. This obviously is not true for all devs, but I am willing to bet that many will shy away from using AI for that reason.
That being said: cleverly using AI isn't bad either as such. It is, after all, just a tool. It depends on what you make with it. And with LLMs or AI graphics or music, working to get the right prompt is an art in itself. Yes, we are swamped with AI games made without love or care, but you can use it properly.