Is all of it from mainstream media? I feel like the different medium has it's own quirks and youtubers are picking it up from each other. The "talking directly to the audience" doesn't really have an exact parallel in TV, film etc. The Youtube person in front of the camera and viewer in front of device has a much more 1-to-1 feel. I might not be noticing it with TV however.
Each medium has its own underlying assumptions. With TV, there's a perception of 'broadcast to the masses' that needs to be maintained. Otherwise it could seem absurd, since the viewer *knows* the content is not directed at them specifically. If a TV news announcer suddenly started behaving as if he was talking to *you*, it would either seem odd, or be a deliberate conceit done for comedy or emphasis value.
But youtube does allow for a much more personal style to work. Since really, any given video view really is going to just the one viewer. Never mind that there may be millions more all watching slightly different sync streams. Plus there's the situational association with direct video chat and other personal communications using the computer. And youtube has a comments facility, so to some extent you *can* reply. Makes a big difference to what styles will seem comfortable.
Regardless of that, other methods of attention grabbing such as unusual intonation, pacing, loudness changes, body gestures, background imagery, etc work in any A/V media. There's a virtually infinite variety of possible tricks, with many still to be discovered, I'm sure. And yes, people can pick these up from each other, possibly not even knowing why they work. Someone may have deliberately crafted a new one, complete with controlled audience studies to determine how well it works, but once it's used in the field it becomes part of society's bag of active memes.
My "talking to the audience" youtube technique totally gobsmacked the teachers at NIDA, labeling me the 2nd worst actor they had ever seen. I was so upset, I was shooting for #1!
I don't suppose they mentioned who they considered #1? Would be interesting to know a name, and find out how they could be so specific. Especially if they all agreed on who it was.