LLMs are incredibly good at replicating common, coarse statistical features - which is what backs "looks very convincing at a glance".

If it's a general signal that's easy for you to recognize at a glance, it's a signal that's natural and easy for an LLM to replicate.

They're much worse at making the underlying structure work. Not incapable at all, especially not the modern LLMs. Frontier models kick ass. But it's true that an LLM denies you a lot of the classic "tell at a glance" by its very nature.