Copyright was not a concept hundreds of years ago. And thousands of years ago people even made use of known names to publish their own work or teachers published their pupils work with their name. This is seen in old bible texts and philosophical greek works till the great canvas portrait painters.
Only the printing press made copying an issue. If a painter painted, the painting was the work, the creation. Not the act of creating the idea of the painting.
Later with audio recording, a similar issue came to be. Singing in a tin can is still singing and people were paid to sing, not for the idea of what they sang, or the memory of it.
In English all this is quite obvious in the word "copy" as a noun. You call stuff you bought a copy. Get your copy now.
The reason copyright exists is not to pay the creators better, but to monopolize the coping stuff. It protects one book press from another book press printing the same thing. There was even discussion in music a hundred years ago, if musicians should be paid, after all, they did not make the recording, they just made music. Oh and artists in general are not paid, just becaue they create things and have copyright on those things. You need a commission and that turns the precious art into mere work. Like a street caricaturist, an old fashioned portait painter or a newer portrait photographer. Creating stuff and hoping people will buy it or buy the copyright, nah. You need to be famous for that. I do not see this incentive you described. You are not wrong, either, but I think that while for some artists it might be a feel good thing intheory, it is not a driving incentive for them to create art. Doing art for a living was always hard. And modern self publishing put a lot of "artists" out there, that never ever would have been published.
Now, is all those things applicable for AI training? One could argue that it is transforming your idea into a new medium. Like making an audio recording of a written book. Undoubtedly this new thing has its own copyright and permission has to be asked, because such action is hidden in that phrase all rights reserved.
But what about an audio description of a painting? Would that qualify for a thing that needs permission and is a right you can reserve? Or simpler, what about a text description? With a complete movie, obviously there is a point where your description is no longer a description, but a transformation into a new media.
People tried to abuse copyright to censor critiques that talked about their works. Because if you talk about things, you, well, have to talk about it. And this makes it necessary to include ideas, concepts and even excerpts from that original work.
Ideas are very hard to protect and this brings me to what actually happens in AI training. The neural net learns what an idea looks like and connects it with words. If later prompted with words, it can recreate similar things.
You can attack this on three basic portions.
1. The finished product. This is easiest. Plagiarizing is forbidden, if you do it with a pencil, photoshop or an AI. Does not matter. Same for those fan games. Either they fall under fair use, or not.
2. Cheaply made products and thus competition. This is annoying, but the way of technology and outsourcing. Also has nothing to do with AI.If you lose commissions to sweat shops or to an AI, you still lose those commissions. Or, gasp, some of those basterds who put their art out for free.
3. The training method of the AI.
Even if 3 would be considered a valid and legal obvious and ethical concern, it is shortsighted, because one could and will just train new databases with ethically and legally aquired material. What then? This has happened in software several times. People just build things from scratch and put you out of business into oblivion anyways.
I remember courts that are technological illiterate and even considered the retaining in memory of a browser viewing content as a copyright violation. So I were careful to be hasty about ethical and judical decisions about all this. It might even need completely new laws.
Anyways, one could claim that the database contains a copy of the original work, wich could be forbidden. And you could claim that training an AI is a form of derivative work that needs approval, like having a translation into machine language or a transformation from one medium to another.
To my legal and technical understanding, there are some AI that do retain copies in their database. But this might be splitting a hair, like those browser problems.
But I currently consider the training of an AI not a derivative work. I consider it machine learning. And since you can't forbid a human to learn from viewing your art, and even create works inspired by your ideas, I need good arguments to forbid machines to do it.
An obvious one might be a paywall. Paying for a movie ticket does not entitle you to bring your camera and make a recording. But on the other hand, I could make a similar movie after seeing it.
Software is easier, because it has licenses. You can forbid commercial usage for example. Actually, one could license art, but can you license the idea of art? You can protect the copy of the actual art, but not the idea. The three wolves moon t-shirt comes to mind.
https://en.wikipedia.org/wiki/Three_Wolf_Moon
I could not reprint that image on a mug and sell it without permission. But do I need a permission to make a t-shirt with a couple wolves and a celestial body? I would say, nah, that can't be protected. Or can it? Should it?
I think the easiest legal way would be to include the permission of usage for AI training in those rights reserved. But this circes back to the point, if this permission is needed. It would be needed, if we dogmatically require it, just because.
But would it be required by current laws? I say, no. Because it would be trying to copyright ideas.
You can protect a specific thing, but in those cases that you do be able to protect an "idea" (see patents in software and other nefarious things), it would only protect against the creation of a similar idea (a blatant plagiarism), and this would be indipendant of the method used.