According to Aonuma, Nintendo recently discovered "several new possibilities" that could make Zelda a better game on Wii U. Thus, the company is taking more time to realize those ideas.
"Since I declared at the Game Awards in December that the game would launch in 2015, the directors and the many members of the development team have been working hard developing the game," Aonuma said. "In these last three months, as the team has experienced first-hand the freedom of exploration that hasn't existed in any Zelda game to date, we have discovered several new possibilities for this game."
"As we have worked to turn these possibilities into reality, new ideas have continued to spring forth, and it now feels like we have the potential to create something that exceeds my own expectations," he added. "As I have watched our development progress, I have come to think that rather than work with meeting a specific schedule as our main objective, and releasing a game that reflects only what we can create within that scheduled time, I feel strongly that our focus should be to bring all these ideas to life in a way that will make Zelda on Wii U the best game it can possibly be."
"So I must apologize to all of you who were expecting the game by year's end, but we are no longer making a 2015 release our number one priority. Instead, our priority is to make it the ultimate and most complete Zelda game. I hope to use the added time to make a Zelda on Wii U that will reward you for your patience. So that you for your continued support."