...is owe to the human nature.
Surfing forums, blogs, facebook, and chatrooms, it seems to me that many people want to let their opinions be heard yet do not have anything to substantiate their views.
Like, for example, a simple statement of "you suck".
An argument would require elaboration and support. But not a statement of "you suck".
Granted, this means such a two-word sentence is utterly useless and meaningless, but that is what many people like to write.
And they want themselves heard.
And what better place would that be other than Twitter?
And diaries, yes diaries, for the exhibitionists that's what blogging is all about. But some blogs I've seen have their majority of posts a few sentences long. Either lack of expression skills or a boring life. Twitter is a good replacement for blogs.