Artists lose first copyright battle in the fight against AI-generated images::But the fight may not be lost as the court allowed the artists to claim copyright infringement against Stability AI, Midjourney, and DevianArt, on workpieces that the artists had filed a copyright for.
In the US, copyright is implicit. All work is instantly protected by copyright the moment it is created. Registering with copyright office is optional/voluntary. I think the judge’s comments that you are referring to was probably referring to the works where copyright protections were waived by the artists for works placed into public domain (which, on Deviant Art, covers a vast amount).
So especially poor and young artists get exploited. Why am I not surprised.