>I think these LLMs (without any intention from the LLM)hijack something in our brains that makes us think they are sentient.

Yes, it's language. Fundamentally we interpret something that appears to converse intelligently as being intelligent like us especially if its language includes emotional elements. Even if rationally we understand it's a machine at a deeper subconscious level we believe it's a human.

It doesn't help that we live in a society in which people are increasingly alienated from each other and detached from any form of consensus reality, and LLMs appear to provide easy and safe emotional connections and they can generate interesting alternate realities.