Does not scale in the way that the day has limited hours, extra work might be okay for a few courses, but not for more because you simply run out of time. There's also the issue that that extra work is given the same grade in the end, but you've spent more time. And no, knowledge doesn't make things take zero time.

Plus, the extra work is still about the same course material - instead of one hello world you write two. It's not hard, it becomes depressing and demoralizing.