And yet they don't, quite a lot of the time, and in a random way that is hard to predict or even notice sometimes (their errors can be important but subtle/small).
They're simply not reliable enough to treat as independent agents, and this story is a good example of why not.
Second, whether they're perfect at following commands is besides the point. They're not just "predicting tokens," in the same way you're not just "sending electrochemical signals." LLMs think, solve problems, answer questions, write code, etc.