I don't think LLMs are sapient, but your argument implies that creativity is something unique to humans and therefore no machine can ever have it. If the human body IS a machine, this is a contradiction.
Now, there's a very reasonable argument to be made concerning the purpose of copyright law, but "machines can't be creative" isn't it.
Selling human livers and selling cow livers are never treated the same in terms of legality. Even the difference between your liver and that of a cow is much, much smaller than the difference between your brain and Stable Diffusion. I'm sure there isn't single biochemical reaction that is unique to humans.
It is however general agreed on those do not create independent original works. At the most generous interpretation they get defined as derivatives, and at the more common interpretation they are plain copies. The creativity is also usually not given to the machine, but those who built the machine. Even if the programmer is unable to predict all outcomes of creative written code, a unpredictable outcome is still attributed to the programmer.
Remember the monkey selfie thing? https://en.wikipedia.org/wiki/Monkey_selfie_copyright_disput...
It was ruled that our Copyright Law does require that a Human create the work, and that only a Human can hold copyright. The monkey was not given copyright over the image it took.
Monkeys obviously can be creative. However, our law has decided that human creativity is protected by copyright, and human creativity is special within the law. I don't see any contradictions or arguments about sapience that are relevant here.