> Is it all that different from asking why someone painted something when AI could generate an image of a painting for you?

I don't agree. In this case it's asking AI to analyze the high-res photos of Van Gogh to learn what paint he used, what techniques, how he held his pencil and how did his strokes look like.

Sure, you could then also ask to paint one for you in similar style, but that's not what is being suggested here.