1) the artist is not literally copying the copyrighted pixel data into their "system" for training
2) An individual artist is not a multi billion dollar company with a computer system that spits out art rapidly using copyrighted pixel data. A categorical difference.
On 1, human artists are copying copyrighted pixel data into their system for training. That system is the brain. It's organic RAM.
On 2, money shouldn't make a difference. Jim Carrey should still be allowed to paint even though he's rich.
If Jim uses Photoshop instead of brushes, he can spit out the style ideas he's copied and transformed in his brain more rapidly - but he should still be allowed to do it.
They probably aren't doing that. Studying the production methods and WIPs is more useful for a human. (ML models basically guess how to make images until they produce one that "looks like" something you show it.)
(That's as opposed to a large language model, which does memorize text.)
Also, you can train it to imitate an artist's style just by showing it textual descriptions of the style. It doesn't have to see any images.
And the weights. The weights it has learned come originally from the images.