The real problem lies in the fact that those non existing citations will become real. Several years back there was a case of an article in Wikipedia that made some unsrourced claims->Journalist that doesn't do verification republishes those claims (without specifying wikipedia as srouce) -> Wikipedia article gets challanged for lack of citation -> the News story first based on wikipedia becomes the reference in the original Wikipedia article. Full circle

It's easy that something like this happens again. chatGPT confidently listes hallucinated sources->media rushes to publish the scoop -> now you have real "sources" for future reference