You know this is an excellent question! I have been wondering about precisely this sort of thing for a very long time. I see this a lot from hubbers I KNOW to be highly educated and literate; I am certain they would never write in such a way outside of the Internet.
I'm talking about starting sentences without capital letters. I'm talking about dreadful run-on sentences, and the like. As for people whose literacy and education I'm not so sure of the output is even WORSE! I would see this and think to myself "What is this world coming to. Oh well, here's proof positive of America's "crumbling educational system," and so forth.
It never occurred to me that they may be doing this deliberately. In a way I'm relieved; things are not quite as dire as I'd feared.
I agree with skisy, whose answer I'm about to vote up soon as I'm finished. It is cool to be smart and educated and to know how to write and speak with vaguely sophisticated grammar and diction, and so forth -- without "putting on airs," or anything like that, you understand.
As skisy said, if an article (and I think one problem is that some hubbers DO NOT think of their hubs as "articles," which they should; they think of them as mere "hubs" that aren't important except as traps for clicks and therefore money) is full of mispellings, non-sequiturs, serious grammatical mistakes, and the like, I'm going to find it nearly impossible to read the piece from start to finish.