What causes people to latch onto a key word and repeat it ad nauseum?
amongst others. It's probably likely these are perpetrated by the same person.
But I really do wonder. Certainly that is not mentally healthy to behave like that.
I think they must feel deeply inferior and unable to make themselves heard in regular conversation. They don't feel like anyone will listen to them unless it is out of annoyance.
If I had to act like an advertisement to get a reply I'd feel like I had failed as a human being.
Memes are the informational equivalent of genes. In the real world, genes that are not adept at survival will fade out. Genes that positively effect the reproduction of the organism are carried over.
As this analogy carries over, memes that exhibit traits that make them very easy to reproduce (think "easy of use" as well as "information to effort ratio") will be reproduced more and more.
This, however, does lead to a "downward spiral" as the environment; the "meme ecosystem" keeps becoming more and more laconic. So whereas in years gone by, a "meme" might be an image macro or a funny face, and to reproduce it you had to have and know how to use Photoshop, the higher rate of turnover and those external forces have pushed memes further and further down, to now they are naught but short bits text, ready to go in any context.
The extra-internet forces, like Twitter's natural 140-limit also forces people to be leaner with their typing, and they're not use to it. Additionally, the overt social-pressures added by things like Facebook (as it stands, your Internet "Profile") have forced people to become less and less offensive in their thoughts, for fear of ostracization, which feeds back into the newer laconic-model of internet speech. Speak fewer words, and there is less of a chance of offending someone.
And now we have "emojis," even going into the dictionaries of the world. Pictographics that convey nothing but feelings.
If you're worried that people on 4chan are replying to anything you say with "Reddit" or "Fedora," you're going to feel much, much worse when 90% of the posts you see contain no text at all. Just a smiley-face and confetti.
Darmok and Jalad at Tenagra.