YouTube belongs to Google. I too wonder why Google hasn't focused more of their attention on YT. It's their social network hub that works fine for about one billion people.
Do the G+ comments below YT videos make sense? No (from the users point of view) . There used to be insightful replies to YT comments including video-replies. All that has vanished, only spam remains. Beside that, anyone remember their older social hubs Google Buzz and Orkut?
But I was kind of waiting for Youtube competant from Facebook for sometime now. I think Facebook is one of the major sources for Youtube and FB has ability to do something about it.