>>494362Photography isn't a derivative artwork.
Your criticism might be more valid by saying sampled music, such as that created by the avalanches, isn't art. That was a popular debate at the time.
However small samples and even long ones have mainstream acceptance in music nowadays. The difference is an artist made something using other people's art, versus the machine making it. The difference is who controls the creative process. A prompt isn't creative as an art piece, it's creative as a prompt.
Best I can do to explain it.