Papers teach people things. You can't really hand someone some working code and expect them to iterate on it to produce something novel and insightful, because it won't be written in a high-enough language to express the core concepts flexibly.
I don't see how that's related. There are loads of open source software projects that are maintained by only a single person precisely because they haven't bothered to properly document why it exists, what came before it, what important things it is demonstrating, or what needs to be done to improve it; the archetypical content of a research paper.
