Because in its brevity it loses all ability to defend itself from any kind of reasonable rebuttal. It's not an actual attempt to continue the conversation, it's just a semantic stop-sign. It's almost always used in this fashion, not just in the context of LLM discussions, but in this specific case it's particularly frustrating because "yes, you're holding it wrong" is a good answer.

To go further into detail about the whole thing: "You're holding it wrong" is perfectly valid criticism in many, many different ways and fields. It's a strong criticism in some, and weak in others, but almost always the advice is still useful.

Anyone complaining about getting hurt by holding a knife by the blade, for example, is the strongest example of the advice being perfect. The tool is working as designed, cutting the thing with pressure on the blade, which happens to be their hand.

Left-handers using right-handed scissors provides a reasonable example: I know a bunch of left-handers who can cut properly with right-handed scissors and not with left-handed scissors. Me included, if I don't consciously adjust my behaviour. Why? Because they have been trained to hold scissors wrong (by positioning the hand to create opposite push/pull forces to natural), so that they can use the poor tool given to them. When you give them left-handed scissors and they try to use the same reversed push/pull, the scissors won't cut well because their blades are being separated. There is no good solution to this, and I sympathise with people stuck on either side of this gap. Still, learn to hold scissors differently.

And, of course, the weakest, and the case where the snark is deserved: if you're holding your iPhone 4 with the pad of your palm bridging the antenna, holding it differently still resolves your immediate problem. The phone should have been designed such that it didn't have this problem, but it does, and that sucks, and Apple is at fault here. (Although I personally think it was blown out of proportion, which is neither here nor there.)

In the case of LLMs, the language of the prompt is the primary interface -- if you want to learn to use the tool better, you need to learn to prompt it better. You need to learn how to hold it better. Someone who knows how to prompt it well, reading the kind of prompts the author used, is well within their rights to point out that the author is prompting it wrong, and anyone attempting to subvert that entire line of argument with a trite little four-sentence bit of snark in whatever the total opposite of intellectual curiosity is deserves the downvotes they get.

Except this was posted because the situation is akin to the original context in which this phrase was said.

Initial postulate: you have a perfect tool that anybody can use and is completely magic.

Someone says: it does not work well.

Answer: it’s your fault, you’re using it wrong.

In that case it is not a perfect tool that anybody can use. It is just yet another tool, with it flaws and learning curve, that may or may not work depending on the problem at hand. And it’s ok! It is definitely a valid answer. But the “it’s magic” narrative has got to go.