Because it has essentially no logic system whatsoever. It doesn't have any way to "know" something is correct because when it produces a word for word copy of a factual statement, it is internally identical to a completely made up (hallucinated) sentence... because both are hallucinated. The deriding "it's fancy autocomplete" remarks are, in a lot of ways, technically correct.
You can still do useful things with it, that much is extremely clear. But it doesn't think.
You can still do useful things with it, that much is extremely clear. But it doesn't think.