I'm not sure I follow that first sentence.

Fair use is an affirmative, positive defense to liability under the Copyright Act. It only exists as a concept because there is a marketplace for creative work.

That marketplace, the framers of the Constitution would suggest, only exists because the Constitution allows Congress to grant exclusive licenses to creative Works (i.e., copyright protection). In other words, they viewed creative work as an driven by economics; by securing an exclusive license to the artist, she can make money and create more art.

I am of the belief that even if there was no marketplace for creative work (no exclusive licensing / no copyright laws), people are still inherently creative and will still make creative things. I think the economic model of creativity enshrined in the Constitution is what gives us stuff like one decent movie followed by four shitty sequels. We have tens of thousands of years of original artworks, creative stories, songs, sculptures, etc. The only thing the copyright clause does, in my view, is concentrate the profit from creativity into the hands of a few successful artists or, more likely, a few large employers, such as George Lucas or Walt Disney, Viacom, Comcast, etc.

I think this unjust enrichment claim comes as close to anything as data dignity that I've heard of. It's not a lawsuit to enforce a positive legal right, but rather an plea to the court's equity to correct a manifest injustice and restore the parties to a more just position.

That the AI companies have been enriched at the detriment of the artists seems obvious. What makes it unjust is that the defendants had no permission and did not pay the artist.