someone who paints in the style of Michelangelo or Studio Ghibli does not pay royalties to either of those entities

I think it's actually not entirely true. There is a thing called "trade dress" (part of the trademark law), which can protect certain design or "look&feel" elements of any products a company produces; the requirements for this are a bit strict, but if the "style" of your painting is sufficiently similar to a Ghibli animation to cause confusion for customers (e.g. someone may reasonably think that the painting is by Studio Ghibli), there is a possibility that it's a trademark violation. But this is also beside the point.

if someone reads ten thousand books and then writes their own story, they are not committing copyright infringement.

There is a legal distinction between human learning and LLM training.

The neural connections in someone's brain formed by reading a book are not considered to be a derivative work, because they are not a "work of authorship" as they are not “fixed in any tangible medium ... from which it can be perceived, reproduced, or otherwise communicated", and they are not “sufficiently permanent or stable to permit it to be perceived, reproduced, or otherwise communicated for a period of more than transitory duration".

LLM weights meanwhile totally fit the definition of a "work", stored in the medium of a digital file (fixation) and produced by humans through a computational process (human authorship), making it a derivative work of the training material by definition.

Once again, I agree that this is actually unfair, but it is the consequence of the law as written, because the law itself is unfair.