Ultimately that's because it's not a knowledgebase. It's not referencing facts, it's referencing sentence structures. The way they've built ChatGPT is very much to convince you that it's 1) a mind and 2) a knowledgebase. Cause that people will pay for.
You ask it questions (requests for information).
It pauses and produces results that look like a person typing (mimic something with a mind).
But it's just filling in statistically likely words next to each other.