While I agree this can be true in general, this is not often the case.
We do mandatory code reviews in our company, and at least a couple of times, I have received a comment which made me go "whoah, this is much better than my idea!", followed by a new version which is 10x shorter and way more reliable.
Being the author of the code in question, I can tell you with full authority that sometimes:
(1) no, I had no thoughts of fixing the code, I did not know it was non-optimal.
(2) no, I had no good reason for not getting around to fixing it. I had no special requirements that would justify my decision.
(3) yes, I just did not think about it. It is like searching for something for a long time and then suddenly finding it in the obvious location -- except this time, I did not find the obvious solution, so I almost ended up committing this huge code monstrosity.