I think because we're addressing a different point. Of course it's good to learn more about how humans work and help students to learn but there has to be a scope in it. Hopefully learning is about being curious, discovering new things, playing with the mind. Metrics won't help bored students, they'll just learn to flip the pages at the right time while watching TV. And now interested students get distracted by the same concerns of being over-watched and not doing the same thing. It's really a terrible solution.

If you want to collect metrics then make them as a personal tool. Make a utility for the student, that only him can access, that helps him learn about his studying patterns, give him hints, ... If they want to share them it's on their own term.