We already have laws covering close derivatives - in this case it might not be clear who is the inspiration but there is no novel creativity... everything these networks produce is derived from artists - there is no added novelty.
I think that's exactly the sort of flawed analysis these copyright trolls do. They see something they never would have had a hand in and count it as "theirs", and then greed kicks in. It's like the old MPAA/RIAA calculations of lost revenue that assume someone would have bought a CD if they didn't download a song. Only worse because at least in the downloading case, they are a 1:1 substitute.
In almost all cases I'd guess that artists whose style is being copied by many genAI users are getting way more exposure than in some alternate universe where midjourney didn't exist. But nobody looks at it that way, they just see somebody else making profit and think they deserve some.
it's derived from the original and competes with the original
if it was parody or commentary or otherwise found a new market, it might be allowed under fair use, but the fourth factor of fair use concerns the effect on the market value of the original