An interesting fundamental limitation of transformer LLMs is that their architecture doesn't allow for the option for the model to choose to think a bit more or to choose to review their answer, as the quantity and structure computations they'll do is fixed in the architecture without any conditionals - but you repeating the same prompt means that the model gets to run a second iteration while having the result of the first iteration as the input data, and that can enable it to do more.

Of course, if we'd want to generalize it, we should have a structure where the model itself can actually make the decision to continue work for one more iteration, and also ensure that it can retain some of the temporary work-in-progress notes (currently it can see only what the previous iteration output as part of the answer).