They feel threatened. And so they attack her. But in attacking her, they make people wonder what the fuss is about, putting her book Atlas Shrugged at #18 on the Amazon best seller list this week (#2 if you just look at the literature/classics category).
I think it was Napolean who said "Never interrupt your enemy when he's making a mistake".
A thread from Objectivism Online: Atlas Shrugged Amazon book-bombing Help send the book to #1 on bestseller list