I'm a mathematician who's been following this stuff for about a decade or more. It's not just expensive. Generative neural networks cannot reliably evaluate truth values; it will take time to research how to improve AI in this respect. This is a known limitation of the technology. Closely controlling the training data would certainly make the information more accurate, but that won't stop it from hallucinating.
The real answer is that they shouldn't be trying to answer questions using an LLM, especially because they had a decent algorithm already.