Because the vast and overwhelmingly majority of the time, if you ask a question into the ether that nobody has a good answer to, most people will gloss over it

Because the vast and overwhelmingly majority of the time, if you ask a question into the ether that nobody has a good answer to, most people will gloss over it and not bother answering, as attested by decades of relatable memes ( https://xkcd.com/979/ https://xkcd.com/979/ ). In contrast, the chatbot is trained to always attempt to give an answer, and is seemingly disincentivized via its training set to just shrug and say "I don't know, good luck fam".