The problem might be that it cannot backtrack. When AI generates output, there is no backspace key for it - it uses "No, but wait!" all over instead, which is very different to human output.
Subagents and/or branching conversations are presented as the solution to this - if you can't backtrack, then branch off a conversation to explore multiple paths (discarding the ones that didn't pan out), but this is a fix in the harness not a fix in the model. It's also literally how we made chess-playing engines back in the 80s: recursive path exploration with a fixed depth.
Humans don't exactly work that way either, AFAIK. So we have this uncanny valley of intelligence: it's some sort of intelligence, but not as we know it.