Maybe it's because they are trained on Internet comments, and the most rare thing to find on the Internet is someone admitting they don't know something.
But if they had been trained on comments saying "I don't know", they'd probably act the same as they do now but they'd treat "I don't know" as the answer.
This is such a 2024 take. Model will push back and tell you the knowledge gap they have, but people are just used to ask gooogle leading questions, which port badly to llm as it makes them defend the position instead of research data
The saddest part is when people take their experience with Google's idiotic AI implementation and assume that's how all LLMs work. Frontier-class models will, in fact, generally admit when they don't know something. That includes the one I run at home on my own graphics cards, but it seems that Google just doesn't GAF.
Your point about "predicting the next word" mostly means that your post was very easy to predict.