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long answer:
because it had a great story one of the best in the series so far, it had great character development , it had the best boss fights of the series and ******** it a feature that allows you to at will fight them again and again , a kick a** combat system , motions gaming that was more then just a flail game ( which was the main intention from the start so from a point of view of some one that actually WANTS to see good motion gaming its a plus ) . over all a great game , not necessarily Best zelda game ever( personally ocarina of time aint ether XD ) but definitely not as bad others make it out to be .

straight answer:
because they did not just judged it as another motion game of the past and actually figured out how to play it

ALL THE GAMES!
Just kidding. I like Twilight Princess and Skyward Sword. e w e;
Majora's Mask was nifty, too. But sad. xD And I like Ocarina, it was just so long.. xD;; And the first ones, all 8-bit.. Bah. I just couldn't get into them. xDD I'm still playing Phantom Hourglass for the DS though. xD

True, all I've heard are bad things,

Ocarina of Time!
The design, the storyline, enless playing, everything was awsome! To me its like the begining of everything before they start rencarnating n blah blah blah
Wind Waker
It was okay. Not bad and not good. I like how he had a little sister and how everything came together (link and zelda meet yet again)
Majoras Mask
OMGosh that games was pain first time I played but I was so determin to know how the game and story goes. I do love the masks tho its creepy and not to childish.

In my opinion (like anyone cares) all the Zelda games were original, well thought out, and just badass! It was then when the hourglass cameout that I lost all sense. It seem childish tho I was intrested in it and its not that bad but I think after that (with the exception of Twilight) Zelda games went down hill (slighly). There're just not the same anymore I suppose too kidish. Ds is kiddish grapic. Dont rant I do love some ds games.

Carry on.