They're not novel, but a poster for a spring fair isn't supposed to look like a de Kooning.
These arguments are almost completely detached from reality. Most artists aren't diverse either - they're told to find a style and stick to it, and that's what they do.
Commercial graphic designers are more versatile, but the set of standard looks is still relatively small. Hollywood movie posters and book cover designers are notorious for reusing the same tropes and colour systems, and that's been true for years, long before AI was a thing.