Why All the Hate?
People really hate Stephen King. One difference between him and a lot of people who've been on these lists so far, though, is that most of the hate directed at Stephen King has to do with his work. Nobody argues that Barry Bonds is bad at his job, for instance, but people say that about Stephen King all the time. For every masterpiece he's cranked out, someone can rattle off the names of five more stories or books that he's written that are absolute junk. He writes about the same things, he uses the same formulas, he gives too much backstory, his books are all hundreds of pages too long ... that kind of thing.
And honestly, a lot of those complaints are valid. Especially those gripes about his books being too long. I don't even want to crunch the numbers that would reveal all the magical and wonderful things I could have been doing with the free time that I spent reading about peripheral characters' relationships with their relatives in the unabridged edition of The Stand. So, trust me, I get that part. I just think that Stephen King's got a perfectly legitimate excuse for all of those "flaws."
Why He Doesn't Deserve It
Stephen King is insanely prolific. Here's a page listing all of his written work. You could read a novel in the time it would take you just to click each of those links. Given the rapid-fire output of his work, it should come as no surprise that Stephen King often strikes out. And since he loves baseball so goddamn much, let's stick with that analogy for a second and consider the career of Reggie Jackson.
Do you mean ... haunted Reggie Jackson?