There are already more great artworks in the world than any human being could appreciate in a lifetime, works capable of satisfying virtually any taste imaginable.
Conclusion
Modern artists are wrong to think that their art lets people get more aesthetic joy than they would get without that artwork. (The works of modern artists don't give people more aesthetic fulfillment than they'd otherwise have)
Evidence
There's such a surplus of great art in the world, more than you could ever consume in a lifetime and capable of satisfying virtually any taste.
Evaluate
Jeez, man. You're giving me a lot of FOMO here.
How can we accept this premise but fight the conclusion and somehow argue that the works of modern artists do provide some aesthetic fulfillment that wouldn't otherwise be satisfied?
This is a really tough riddle for me to crack. If you think about music, as an example, does any new song fulfill an aesthetic need we couldn't have otherwise fulfilled?
An exotic counterexample that comes to my mind is to argue that if you don't have access to internet, you don't have The World's Great Catalogue of music available to you.
You live in Antarctica or the Galapagos Islands, and you miss your Swedish death metal. You can't get it online. You don't have it with you. Then, what's this? Sven, who works at the same lab as you, shares his artwork with you. Lo and behold it's Swedish death metal. You two sit together at the lab cafeteria forevermore.
Goal
Find an answer that is less stupid than that, but similarly allows us to argue that even though more than enough great art exists there's still some way for a modern artist to be useful in a way that provides someone with something they wouldn't otherwise have.