Publishing is changing. It used to be that the normal publication cycle was a hardcover release, followed by a mass market paperback. Our publisher is Orbit, for the Expanse series and Daniel’s Dagger and Coin. In the US, they do a simultaneous release of trade paperbacks and ebooks, with no hardcover release. Ebooks are killing the mass market paperback, as they take the role of the disposable book. Trade paperbacks don’t suffer from the frankly stupid stripping returns rules that mass markets do, so they make more sense for physical copies. And hardcovers are expensive and are less likely to be impulse buys.
All that being said, though, there are people who just like hardcovers. If you are one of those people, and would really like a hardcover of Leviathan Wakes, the only place to get it (right now) is the venerable Science Fiction Book Club. I have two hardcover copies of Leviathan Wakes that I bought through the book club, and they look great. The club is also going to be releasing hardcover editions of Caliban’s War, so if you want a matching set, they’re the place to go.