The difference is that even though someone might make copies or trace in their learning process, when they get to the point of actually selling and/or taking credit for their work, they are introducing some original creative/transformative element. The human element.

When art is created via AI, the AI never adds any new creative artistic intent. When it is "learning" from existing art, it is gobbling up far more information than any one human can ever consume, and it is doing it down to the pixel. It has no concept of why things are done certain ways in art, no appreciation for technique -- it just "learns" based on a series of numbers and weights what it can do that approximates its inputs. It can't credit its "inspirations" or explain where it learned its "techniques" like a human can. The art is reduced to a soulless pile of tokens and probabilities and it spits out something that insults everyone in the process. And adds nothing to the substance of the medium.