Even if true wiki would escape via fair use and AI would not.
It is possible that the laws and judgements are inconsistent nonsense but assuming they are not the fact that wiki has been around for decades suggests at least one key difference.
Just because Wikipedia has persisted for 20+ years doesn't mean that a key decision later down the line can't make it into an open season for all IP owners. AI-related lawsuits are a great opportunity for copyright owners to greatly shake up the status quo under the (fairly legitimate) guise of protecting themselves from LLM copying. Even if Wikipedia in particular could skirt it through fair use, the fact that hundred-word long summaries would be found "similar" to full novels would represent a large encroachment of copyright that would allow many other lawsuits to open up with entities who may not be as lucky as Wikipedia. Changing the answer to "Is something as brief as this notably similar to a full work?" from "what? Of course not" to "well... do you have a fair use reason?" would mean that many people will need to start looking both ways and triple-checking whatever they create/summarize/report on as to avoid tipping off anyone hungry for some settlement money.