It just gives the audience a clearer picture of the artist's process. I'm not saying artists (and btw I'm an artist) need to disclose every piece of reference they use for everything, every time. However many artists do share their process, and the way in which reference is used can vary greatly. Many artists use reference to practically copy the subject, others just use reference to understand the subject and then create something completely different. Or in a completely different pose.

As someone consuming art, I would appreciate knowing what type of mastery and skills the artist has- did they envision this in their minds? How much? What inspired them? Is this an accident or deliberate? Etc. This may be irrelevant to some people, but many at some point want to understand how the artist thinks and feels.

Before AI it would have been obvious that if the subject is not realistic and not found elsewhere then it has to be the artist's imagination, or an accident. Now an artist could be copying AI instead and you would never know.

I find that artists that tend to copy their references with high fidelity (such as many wildlife painters or illustrators, or personal portraits) are also among those disclosing their references the most. This makes the audience appreciate the artists' skills more. You can see the difference between the original and the result whereas you would otherwise have to guess.