On the one hand, I get that people find journaling prompts worthwhile. So it seems to me that ways to generate them might be worth doing. And indeed, you can find a great variety of products that provide that: https://www.google.com/search?q=journaling+prompt+products
So I get that some sort of AI-driven way to provide better or cheaper prompts could be good.
But to me this is drawing on our built-up reaction to actual humans writing actual prose. And in the process, undermining that. Sort of the same way that spam is not just a problem because of the individual pieces of spam, but because they degrade the perceived value of the medium as a whole. Or like how the artificiality of a manager-driven icebreaker read off cards can push people apart rather than bringing them together.
So what I'd rather see is some AI product that solves the same problem without pretending to be human.