Also, LLMs are essentially designed to produce code that will pass a code review. It's output that is designed to look as realistic as possible. So, not only do you have to look through the code for flaws, any error is basically "camouflaged".

With a junior dev, sometimes their lack of experience is visible in the code. You can tell what to look at more closely based on where it looks like they're out of their comfort zone. Whereas an LLM is always 100% in its comfort zone, but has no clue what it's actually doing.