People ask this because it's an invitation to eat with someone without the respondant having to admit that they are would like to be fed, which could be consisdered as implying that their host or whatever is being negligent to the needs of their guest. It is a little silly. But, and I am a ND person who has learned a lot of this by trial and error, there are deep instinctual behaviors that these rituals are about. I'm not here to say whether or not any of this is good or not, but especially the rules about hospitality strike me as things that got ingrained into culture in order to make common uncomfortable situations more reliable by the means of rituals that people follow or don't, indicating whether or not they're someone who is going to play their prescribed role - this is maybe why there are often many ritual refusals and acceptances. It's a way to play-act giving someone something that historically might have been precious and if they don't play along, you can weed out people who are likely to take advantage of you. It's imperfect of course and not considerant of neuroatypical people, but it just kind of had to work well enough to keep going.

It is definitely frustrating to not know ettiquette and I often feel like throwing all of it out in favor of a more direct system. Sometimes I do! But for the rest of the time, I find that ettiquette manuals are super helpful, especially when they explain the reasoning behind otherwise inscrutable rituals.