Going to the doctor for expert advice is often inconvenient, or time consuming, or expensive, or stressful. I think a lot of people want, and seek out, information and advice based on their symptoms, as a first step before a possible doctor's visit. Before LLMs, WebMD (and excessive self-diagnosis based on WebMD) was a meme for a while.

So with regard to LLMs, for me the question is not purely "how often does it get it right?" the question is "how does it compare to the sources and self-diagnosis methods people use otherwise?"

Of course, I agree people should be careful with any form of self-diagnosis or LLM-diagnosis.