MonkeyPaw said in a Facebook note that it wants BurgerTime World Tour to have "a fresh new multiplayer experience, including competitive online play and leaderboards." Features like these require a lot of QA, and therefore the publisher is holding off on the release until everything is stable.
Then, of course, it has to work with Microsoft, Sony, and Nintendo to figure out when they all want the game to go up on their respective storefronts.