> Learning and then creating something new from what you learned isn't copyright infringement, so what's the legal argument here?

The legal argument is that copying or creating what would otherwise be derivative works solely within a human brain is exempt because the human brain is not a medium wherein a configuration of information constitutes either a copy or a new work until it is set in another medium or performed publicly, whereas the storage of an artificial computer is absolutely such a medium (both of which are well-established law), so that the “learning” metaphor is not legally valid even if it is arguably a decent metaphor for some other purpose, furthermore, learning and then creating something new is often illegal, if the “something new” has sufficient proximity to the source material (that's the prohibition on unlicensed derivative works), and GenAI systems often do that and are (so the argument goes) sufficiently frequently used, and known to the service and model providers to be used. Intentionally to do that that, even were the training itself not a violation, the standards for contributory infringement are met in the provision of the certain models and/or services.