The difference here is that Xerox isn't trying to handwave away copyright, while OpenAI et al. are explicitly defending the position in court that LLM output doesn't violate copyright, not that the LLM user is responsible for copyright violations. (I'd be hilarious for them to try to take this stance thought)

I.i.r.c. they even "give you a license" to use LLM output, implying that they own the copyright. Too lazy to look this up so I might be wrong there though.