Either you insist that copyright must be respected at every level, and the creators of material used for training deserve appropriate compensation, or
You throw out copyright completely in this context, but that means the resulting models cannot be treated as proprietary either unless they were produced using absolutely no unlicensed training data.
I think there is an argument for both. Want to create a proprietary model for commercial use? Pay up. Creating an open source, copyleft project exclusively for personal use and artistic expression? Exemption.
The current status quo is perfectly described by powerful corpos extracting rent. Billions for themselves and pennies for the average artist.