And then I realized: it was marketed as a YA version of G.R.R. Martin's Game of Thrones. (It was also mentioned at GreenBeanTeenQueen, which also triggered this post.) Now, I haven't read the books, but I've been watching the show and I can tell you that Maas ain't got nothin' on Martin.
Now, it's not even that Martin's writing style is better. I wouldn't know. It's the fact that comparing Maas' fantasy to Martin's was like comparing apples and tomatoes. It's the same color and roughly the same shape, but once you look inside there not at all the same.
Martin has a high fantasy - you're introduced to a different world right away. There's no denying that Winterfell and the way the world works (winter is coming!) is nothing like Earth. There are dozens of characters that we follow the stories of. The plots are intricate and you can't really figure out what's going to happen until it does.
Maas' story was a light fantasy - the world is very Earth-esque; we only know it's fantasy rather than a medieval story because of the weird names and the continuously-dropped hints on the magic. There's one character who we follow and the plot is fairly straight-forward.
So people going in expecting to see a Game of Thrones-esque story were bound to be disappointed.
So why market it by comparing it to another book? Attaching the name of a bestseller to your book will probably bounce the sales up, sure, but it doesn't hep the book in the long run if the book is nothing like it.
Have you seen any other books recently that do a terrible job at marketing?