Social media I think has had a huge impact on the popularity of YouTubers, which in turn has impacted the popularity of YouTube.
Not sure huge names like Tyler Oakley would be as successful if not for tumblr, twitter etc where people can interact with them. Sure they'd still be successful because social media wouldn't change the video quality of YouTubers, I just don't think the whole YouTuber/fan relationship would be the same.
but also, because of the changing in the way people want to view media has changed into more online than it was has helped too, i think. Why pick up a newspaper when everything is so accessible online? The internet is something entirely different now than it was. I know that doesn't affect YouTube as much and stuff, but if the internet wasn't what it is now, I think maybe it'd be a bit different.