Because until recently (I'm talking last 150-40 years here depending on how we want to define thinking) the only things that could think were various animals. And so 100% of their systems for thinking were rooted in biology. If an LLM can think (and I'm partial to thinking that it can) it's going to different in a number of ways from how a person would think. They may be some overlap, but there will be all these human / biology / evolutionary psychology things which are really person-specific. Even just basic stuff such as seeing faces in the clouds, or falling prey to appeals of emotion. (ie, because our thinking is wrapped up in other processes such as status / ego / survival / etc.) Thinking has only been biological for a long, long time. Non-biological thinking is pretty new, even if you extend it back to the early days of computing.