Previously there was no way to credibly sell an "original". You can produce a commission for someone, but the nature of a digital artwork is that anyone you show it to has the whole thing.

To a certain extent this was already the case with photos, and IMO that's part of the reason that prices for photographic artwork are much lower than other media. You'll sometimes see photographers selling a series of 500 numbered prints (or whatever) as a sort of a way around that, and NFTs are kind of a more digital version of that.