That's not really true.

1) At it's core an LLM is indeed just program - a function. You give it a sequence of input tokens and get back a set of next-token probabilities.

2) By the time you've wrapped the model in a text in/out inference pipeline, and are now calling that from ChatGPT or Claude Code, it really has become semi-autonomous - you ask it a question, or to do something, and until it decides to stop responding it is now in control, even if "it" is really the client or agent not the model itself - just a function.