Would you apply the same rule to a software codebase? Perhaps if nobody can be bothered refactoring that code, it’s not needed anymore and should just be deleted?

Sunset provisions are a pain for anyone who administers the law or makes plans for the future based on it. Laws that depend on the current date are bad, and stable legal institutions are good. That’s why we incrementally “reform” the law, rather than periodically replacing it like some depreciating asset.