That is also the secret of most self-paced online platforms like Udemy, Pluralsight and many others.The metrics they don't like to share. Most users never watch videos until the end, they buy courses but never start them or complete less than 4% to 10% of the course.

You can see sometimes course authors acknowledging these metrics. Companies training departments just wash their hands and say, we have these thousands of courses made available for our employees... :-)

How do you mean? How does youtubing a lecture differ from sitting in the lecture hall itself for example? I'd argue both arent great learning experiences, but lectures seem to be viable enough to make up the bulk of contact time at university

Yes, but it is very very hard to find the personal discipline needed to do so. If you watch mindlessly you will learn very little. If you watch, then do the exercises/practice (depending on the topic different things are needed) you can learn a lot. Almost nobody does, but youtube and classroom lectures that are known to work are very similar - the difference is classrooms have various ways to get people to do the other homework.

I agree with you and upvoted, but saying things like being ready for downvotes is the surest way to get them if only for commenting on downvotes. :)