Because he's not a teenaged Indian-American writing his first amazing book at the age of 17.
It's all about the "wow" factor. Look at Eragon. It's not like anyone (before discovering plagiarism) was lauding "Opal" for its originality, anymore than Eragon was. It's for the youth of the author. "Wow! Look! Isn't it amazing! They're so young!"
(And by the way, most people in the industry that I've talked to think that half a million is entirely too much for someone so inexperienced. Most great authors in YA don't merit that much.)
EDIT: I just read that they'd only shipped 55,000 copies. That's pretty low for a $500,000 advance, even with a second book in the works. They only sold through about 9,600 copies before they pulled the book. Even if she was making a 15% royalty, if they sold every copy on the shelves, she'd only earn out $139,837 of that advance at a $16.95 price point. Of course, I think they were marketing it as an adult, so perhaps the cover price is higher. Dunno. Can't see it on amazon now that it's been pulled--most of the used & new books from other sellers are selling for $12.95, but I don't think that's the original cover price.