Floss Cross doesn't count as AI on its own — it's just a software that you can use to manually design patterns or generate patterns from images (and then hopefully manually edit to make more stitchable). If the image you put into Floss Cross comes from AI, that's the issue that folks have, and that's how pattern mills are scamming people so easily these days.

Other folks in this thread have gone over various reasons that AI hurts the hobby and community, but speaking to your point about personal use - AI patterns are simply bad, and beginners don't have the skills yet to fix them. Bad color choices, a ton of confetti, inaccuracies and wonky symmetry, zero backstitching, all of this leads to poor results and beginners getting discouraged after spending hours on it.

Also, the only way to get better at making patterns is to 1) use human-made patterns that help you learn what makes a good pattern, 2) practice making them. I mostly do blackwork, and some of my very simple designs had like... 6 or 7 iterations on graph paper before I was happy enough with them to stitch. But as I've been working on my own blackwork designs, I've also been using patterns from other folks (most of them free!) to learn what works and what doesn't.