Why? Because this is the reality. One of the so many SEO tactics is to publish own videos to YouTube linking to the original content. Right? Wrong. I learned that any sales videos and your opt-in videos must be kept in your own server. The reality is that your YouTube videos might easily outrank your own website content - your own web property. And if so, why should you do that? Doing that, it might be YouTube displacing you rather than a competitor displacing you. I think it somehow not ethical, but making a choice letting this giant this capacity is everybody’s own fault.
I have alot of sites. In my experience, this only happens when something is wrong with domain that owns the videos. Either Penguin or an unnatural link warning. Whatever it is, fixing it makes it original rank normally again.