Well, I never said anything about one-shotting it.
What I said is, those AI companies push LLMs as the replacement of programmers, that can do everything code-wise, say their programmers "don't write code anymore" etc.
So how come they can't have the LLM write something better than "react for cli" for their flagship agent product?
My only half-decent guess: they deem it too big and risky and believe they'll lose revenue while working on it and ironing out remaining kinks.
Claude Code is likely not well-specified and it's a product of rapid iteration and now nobody really knows how the whole thing works. LLMs don't do well when requirements are muddy.