[saraid216]

It's more layered than that.

If people merely wanted to get the information out there, and make it possible to self-educate, then they would develop... well... wikis. Websites. YouTube videos explaining concepts. And that'd be it: they'd judge their success on outreach, on page views and maybe comments and emails. You'd have Khan Academy, full stop.

But that's not actually all they want. They want to know that their students understood. And to do that, they need to have the student prove their understanding as feedback. That's what completion rate really means. It is the metric that professors and teachers are accustomed to measuring themselves by. They've been trained to recognize the quality of their work based on the pass/fail rate of their class.