Because it seems like for an awfully long time, it's been rather quiet on the news front in regards to this game. No screenshots, no trailers, no official site, no release date... and it's meant to be out this year.
Same with Luigi's Mansion 2. Where's the news? Where's the game info that usually gets released?
The most recent screenshots from Paper Mario are from September 13, 2011, as with Luigi's Mansion 2.... what about Animal Crossing? The same.
But there's nothing suggesting these won't be out in the Summer.
Did we know about Super Mario 3D Land on March 1, 2011? No. Not until March 2, 2011.... yet that was released in November.
But then, NSMBWii was unveiled in June, and released just 5 months later, so... maybe they'll announce the release dates at this years GDC, which is from March 5 - March 9.
Albeit, this is in the US, but it should give us an idea.