Because people can tell the difference between AI art and human art. Not true for logic unless you are incompetent.
AI art is human art. It is based on human intent and choices (and in non-trivial cases it’s a lot of effort to get the machine to produce something that resembles a artist’s mental image), and the rest is mathematically sourced from human art.
I strongly suspect the only difference is in level of decision making, where details that aren’t explicitly planned are randomly generated rather than chosen (consciously or not). Or unable to be planned - refining the generation results is the most difficult part. Which translates to that “sloppy” image.
Humans can detect sloppiness, not “AI”.
There's an insane amount of fine-tunes out there (be it base models or LoRAs), that drastically vary in styles they produce. "AI" art can look very different, and I still think the only common property to it is sloppiness, lack of intentional attention to the fine details.