It’s commonplace for a publisher to release these genre novels in hardcover for the young adult market, then in mass market paperback for adults.

The reasoning doesn’t necessarily fit; they do it that way to maximize sales of each version. They get far more hardcover library sales with books targeted at young adults, and more paperback sales if that edition is targeted at adults (“old adults”?). Even though it’s the same book.

My guess is that they do it this way partly from habit and partly because they expect to make more library sales here, too, if the book is considered a juvenile or YA title.

On the other hand, not only am I not a book publisher – I don’t even play one on TV.