I just think this particular Zelda cycle was exacerbated by Nintendo trying to save Wii U sales. They showed something they were not ready to show, hence us going over a year with nothing but off-screen footage.
Pretty much. It's like how for E3 2009 they just showed that poster for Skyward Sword because they didn't want to reveal footage yet and even for it's grand unveiling at E3 2010, the footage and demo were a few bits of gameplay from the first forest area with some early dungeon elements in because the real game was still over a year away. Back then they could get away with it since the Wii was a sales monster and they already had Twilight Princess at launch so the new Zelda wasn't exactly a huge selling point the console needed anyway.
The footage we saw at E3 2014 for this game was probably of a game that design wise was at a similar spot Skyward Sword was in 2009. But because of the Wii U's terrible hardware sales, Nintendo decided to show more then just a concept poster because they needed anything to help make the Wii U look better. So this year the game was more then likely around where Skyward Sword was in 2010, which was still pretty early which is why we got no real footage except that few second to say it's still a Wii U game as well.
I imagine Nintendo wants this games real unveiling where the title is announced and everything to be a huge event since it's the first open world Zelda and the NX version is probably that systems biggest core game at launch. Nintendo basically want to be able to control the hype for this game and after it's early teaser footage last year, they want to make sure the next real look is when enough of the game is done enough to give people the impression Nintendo wants them too when they see the first open world Zelda. They'd rather have people be angry for a year that they haven't seen any new footage that they imagine will be exciting, then people being angry that the footage they saw didn't look very exciting.