I get that's what you and a lot of people want it to be, but it isn't what they are. They are quite literally probabilistic text generation engines. Let's emphasise that: the output is produced randomly by sampling from distributions, or in simple terms, like rolling a dice. In a concrete sense it is non-deterministic. Even if an exact answer is in the corpus, its output is not going to be that answer, but the most probable answer from all the text in the corpus. If that one answer that exactly matches contradicts the weight of other less exact answers you won't see it.
And you probably wouldn't want to - if I ask if donuts are radioactive and one person explicitly said that on the internet you probably aren't going to tell me you want it to spit out that answer just because it exactly matches what you asked. You want it to learn from the overwhelimg corpus of related knowledge that says donuts are food, people routinely eat them, etc etc and tell you they aren't radioactive.
And you probably wouldn't want to - if I ask if donuts are radioactive and one person explicitly said that on the internet you probably aren't going to tell me you want it to spit out that answer just because it exactly matches what you asked. You want it to learn from the overwhelimg corpus of related knowledge that says donuts are food, people routinely eat them, etc etc and tell you they aren't radioactive.