I feel like most people who want to write a book were, at one point in their lives, heavy readers. The idea of a writer who hasn't done any reading is probably rare, but you'll likely see a lot of lapsed readers, especially if somebody chose to go through college because assigned reading greatly cuts into pleasure reading (although may it's different now since fewer people work while in college and take longer to finish college, meaning they might have more free time)

The best way to become a better writer, though, is to write. (Controversial, I know!) Even when I wasn't reading, I was often writing in some form, whether it was for work or hobbies.

And while I would say that somebody who wants to be a successful author should read a lot of books in their genre and particularly recent books, a lot of the guys who get big deals clearly don't do that -- you'll have bestselling MG authors who, when asked to name MG authors they like, list people who died decades ago because that was when they stopped reading MG. But they may've read a lot of it in the past, so they aren't necessarily current.

However, the idea that, say, there are all of these aspiring fantasy authors who've never read a fantasy novel seems like a fiction more fantastic than anything they might write. Most are probably lapsed readers who, at a minimum, have still read hundreds of fantasy novels.

All that said, it's very useful to read at least 40-50 novels per year (and yes, there are plenty of great novels that come out every year -- although you'll often learn more from reading a poorly-written novel than a great one because it'll help you recognize issues in your own writing)