Projects tend to have an individual feel. Becoming fluent in the language is only a qualification to be involved, but actually coding it well requires an understanding of the idea and overall feel.

Once the project is mature enough, it to some extent drives itself. When that point, that idea, that understanding, clicks, it can be very easy to sit down and code additions to it. Extensions become obvious and trivial. But before that point, there's a lot of time spend on reaching that level of understanding, whether through thinking or the code-erase-rewrite cycle.