I think in your case the problem was multifaceted. First, it was a 3 hour video on Agile. Excessively long, probably boring, probably unnecessary (in my own experience, the agile methods are mostly to get managers to see the light, not the programmers). Second, there was probably little penalty for not watching it either. I've been through Scrum training, it was boring and "successful completion" mostly meant sitting in a room and not doing my actual job for a few days. Failing the course would have required more effort than completing it.

For schools, obviously they'll still be grading your work and ensuring mastery of the subject where not watching the lectures would probably reflect on homework and test scores pretty quickly as you advanced, they're also much shorter than 3 hours, where your attention is less likely to wander.