@ErinnStoriess its most probably as a result of the development in you, as a writer. Now you have an already made plot, already-made characters and a hell of a lot of backstory to build more on. If the very first book is not so much reader-bait, most writers write their second installment even BETTER. As a writer, with a second installment, you have an even clearer sense of not just your plot but your characters too. The first book might be touch and go but if there is a second one, its DEFINITELY going to be better. This reflects in your reader audience and amount of reads you get for the second book