Also, a demonstration isn't worth that much, though better than nothing. There's only so much you can learn in an interview 'demonstration', and I can't afford to give everyone six months or a year to demonstrate what they really can do.

What the YouTube videos demonstrate to me is a lack of effort and committment to find the very best sources and learn the best material; obviously to me, computer science theory and a real professor would be better (skill training is good after you have that, though I'm greatly simplifying here). If that's how they approach their skill-aquisition project, that's evidence of how they'll approach projects at my business. If they follow the herd on that, it's evidence that they will follow the herd otherwise.

I know which way the herd is running. It's not only the wrong way (there's no correlation between herd direction and the 'right' direction - in fact, I'd say there's an inverse correlation because the herd is driven by other things), it's to my competitive advantage to go another way. I want people whose standard is the very best and who think for themselves. And in addition, the social media culture from which the YouTube training trend arises, is highly reactionary, which is crushing to creative, enthusiastic, independent thought.