Because the choice is never, "Should I refactor this code or not?" The choice is, "Should I refactor this code, or work on this feature/bug/refactoring/etc. in

Because the choice is never, "Should I refactor this code or not?" The choice is, "Should I refactor this code, or work on this feature/bug/refactoring/etc. instead?" Sure it could be refactored to be cleaner, but thus far, presumably there has always been something more important to do. Any time this if statement has been edited, it was clearly faster to simply add to the existing one than to refactor the whole thing. Sometimes it makes sense to take that extra time to refactor code when you happen to be working on it anyway... and sometimes there's something else more pressing to do.