I don't get YouTube fads

Here's what I don't understand about those YouTube videos that "go viral" that seem to be entertaining primarily for their complete lack of anything entertaining in them.

Humor is the kind of thing that doesn't withstand dissection very well. If you look too closely at it, almost anything that's funny seems absurd, trite, or unfunny. Keeping that in mind, yes, I can see how it can be funny to watch someone trying to be funny and failing, in some very limited situations. It's a specific case of a general rule that watching someone fail can be funny. (To me, that's a kind of humor that can only be stretched so far. Clearly, the Internet is full of people who have a vast appetite for it. But I can still see how it's a valid form of humor, even if my taste for it runs to the very slight.)

But why does one particular instance of something completely lacking in entertainment value become a viral sensation and have lots of people crowing about it and repeating it and passing it around? The fact is, YouTube is full of thousands, maybe millions, of videos that have pretty much exactly the same quality of having only that entertainment value that can be derived from how awful and completely devoid of entertainment value they are. Why do people find one particular instance more worthy of passing on than another?

I wonder if there's some different quality to the complete failure to be entertaining in one video compared to the others that I fail to discern, which explains it. Or is it just sheer blind luck that one happens to get forwarded around enough to pass some critical threshold? Am I missing something, or is the only thing I'm missing the fact that I'm the only one who cares if he's missing something?