Arguably, it requires the LLM to have access to the source code during training. If it's closed off (like Windows), then the LLM can't train on it.
Even if the source code's old, the fact that it is publicly available makes it much easier to train & improve on than if it were walled off.
Not only training, you can literally clone the source code locally and ask the agent to debug your problem by grepping the kernel itself. Even if doesn't "know" the answer it can investigate it on the fly, that's super powerful