That's easily explained.

It's mimicking human text instead of thinking up questions them formatting them. So if you ask for general trivia questions, it's just sampling from texts it was already fed, thus allowing it to leverage the work humans already did in coming up with decent and sensible trivia questions. But if you ask for specific quizzes then it has either limited or no sample data for that, so it has few examples of good curated questions to ask.

Normally, a human would come up with some interesting fact first, then turn it into a question/answer pair. but ChatGPT just blindly writes a question to start with, then coming up with an answer is an after-thought. It's not even thinking about that while writing the question. So, the questions might superficially look like they're well formatted and grammatical but for ChatGPT no thought has gone into whether an answer even exists, is interesting, or unambiguous.