YA may have blown up over the past decade, but it used to be a small section of bookstores. In the early nineties, it consisted mostly of "teen thrillers," which mostly featured dark mysteries and serial killers, although there was some supernatural fare as well. The authors of those days were ahead of their time and built an audience in teenagers, and paved the way for the YA that is beloved by so many today. All YA books at this time were sold in mass market paperback format, a cheap way to mass produce books for readers. It's the same type of smaller paperback format that many mysteries and romance novels are published in today. They're pretty disposable, and if unsold, rather than ship books back to publishers, bookstores strip the books of their front covers and mail those back for credit, as proof that it hasn't sold. It's cheaper to do it this way than pay for shipping heavy books. In the front of these books, there's usually a warning about