That's not their goal, but it's the inevitable result of the way their comment system is structured: they only show the last few comments, there's no or minimal

That's not their goal, but it's the inevitable result of the way their comment system is structured: they only show the last few comments, there's no or minimal threading, the user base is huge, and the moderation is ineffective. YouTube is a forum for unintelligent conversation, by its very design.