Plus they will take one hour to explain what could take 2 min, just to keep you on the platform....
Once I saw that I realised just how padded the content really was and started looking elsewhere.
Other good tells the content is low quality or a bad fit for video are excessive amounts of talking head (should have been a podcast) or stock video clips (it's video, show me something).
But this was also the joke about TED Talks: everyone came away smugly confident they were part of an amazing tide of progress, ignoring any engineering or scaling challenges.
The reason that 20 minute videos are more popular these days is that more people are watching youtube on larger screens, like on their TV on the couch, and so more reliably watch longer videos than in the past.