It's not really that, it's that recalling a set of rules and following a set of rules are fundamentally different tasks for an LLM. This is why we need, and have implemented different training and reinforcement strategies to close that gap. The chain of reasoning ability has had to be specifically trained into the LLMs, it didn't arise spontaneously. However clearly this limitation can be, and is being worked around. The issue is that it's a real and very significant problem that we can't ignore, and which must be worked around in order to make these systems more capable.
The fact is LLMs as they are today have a radically different form of knowledge compared to us and their reasoning ability is very different. This can lead people to look at an LLMs performance on one task and infer things about it's other abilities we think of as being closely related which simply don't apply.
I see a lot of naive statements to the effect that these systems already reason like humans do and know things in the same way that humans do, when investigation into the actual characteristics of these systems shows that we can characterise very important ways in which they are completely unlike us. Yet they do know things and can reason. That's really important because if we're going to close that gap, we need to really understand that gap very well.