Suppose you get a paper, you automatically implement the code, and then modify it a bit with a novel idea, and publish your paper. Then somebody else does that with your paper, and does the same.. at some point, we will have a huge quantity of vibe coded code on github, and two similar papers will have very different underlying implementations, so hard to reason about and hard to change.
From a learning perspective, you try to understand the code, and it's all spaghetti, and you loose more time understanding the code than it would take to just reimplement it. You also learn a lot by not only reading the paper but reading the authors code where most of the small details reside.
And I'm not even talking about the reliability of the code, test to know that it's the correct implementation. Authors try to make papers as close as possible to the implementation but sometimes subtle steps are removed, sometimes from inadvertance, sometimes because the number of pages is lionmited.
A paper and an implementation are not one-to-one mappings