But humans have vastly lower error rates than llms. And in a multi-step process that means that those error rates compound. And when that happens, you end up with a 50/50 or worse
And, more importantly, a given human can, and usually will, learn from their mistakes and do better in a reasonably consistent pattern.
And when humans do make mistakes, they're also in patterns that are fairly predictable and easy for other humans to understand, because we make mistakes due to a few different well-known categories of errors of thought and behavior.
LLMs, meanwhile, make mistakes simply because they happen to have randomly generated incorrect text that time. Or, to look at it another way, they get things right simply because they happen to have randomly generated correct text that time.
Individual humans can be highly reliable. Humans can consciously make tradeoffs between speed and reliability. Individual unreliable humans can become more reliable through time and effort.