That's because an LLM has no motive, and we're used to automatically guessing people's motives in any conversation. Motives don't have to be nefarious, for most of us, posting on Ars is primarily motivated by boredom, killing time, etc as well as an interest in the subject. If someone was always posting about how Bitcoin is the future, etc etc people would similarly make some assumptions about their motivations.
LLMs have no motivations, so when we naturally try to guess, it comes across as being fake and insincere in ways that are almost baffling, because we aren't used to a conversation without a motive or any operating theory of mind as we know it. And of course, the LLM cannot understand your motivations and won't respond to them as we expect.
