I can't imagine any real purpose for NFTs except money laundry and the 'I Am Rich' complex. With paintings, you're at least getting a physical artifact that the famous painter touched and painted, stroke by stroke, that can never be duplicated. https://en.wikipedia.org/wiki/I_Am_Rich
Let's say we could replicate the painting stroke by stroke. Let's say we also use the same painter. Still, it doesn't matter. A copy is a copy. It's not the same as the first and initial incarnation of that artifact, physical or digital.
Art has its worth because it is difficult to forge, mostly through its proof of provenance, but also through the certification of designated, well-paid experts.