I think it’s because of the presentation aspect, which totally doesn’t translate well into word of mouthing. (since most funny internet stuff, like memes and shit, is born ON the internet) It’s just something you gotta see, or hear online, with all the elements together.
For example, I could tell you right now about this Street Fighter animated series cartoon mashup that really makes me laugh, and where I’m pretty sure there’s a meme of somewhere, just from this one joke in it. But how fun is it that I’d tell you about it, if I could just show you? It’s made to see, not be told.
Since the internet has its restrictions when it comes to presentation, what is put on it makes use of all it can, and usually becomes something novel, at least for those into and understanding the culture. Many online things, obviously, are built around the medium, so it wouldn’t all work in real life too much.
Btw are you familiar with Street Fighter? The video is really hilarious. Check it out if you got ten mins to spare. Get in the plane!
Another personal opinion is that since material on the Internet usually adheres to its medium, you can go really far into subjects and get all obscure and messed up, but in a way that makes sense on the plane in which it resides. (unlike TV, where it’s constantly restrained, at least a hell of a lot more than the Internet. And I don’t mean censorship, but what sells to the public) Just seems nonsensical offline, even if you talk to someone about something specific that they also understand. Am I making sense lol? It’s why knock knock jokes are left offline. It isn’t funny online, just like me describing that video to you in real life wouldn’t be really funny, because I’d have to explain a buncha shit while I’m at it. Even if you know what a cartoon mashup is, I’d still have to tell you that ’‘Vega’s mask sure looks scary!’’ wasn’t originally said during the shot they’re showing when that sentence is said. But if you just watch it, you’ll understand everything right away without any explanation. Some online properties just don’t work into assigning humour some significant factor, and vise versa.